Gas turbine power plant control apparatus including a turbine load control system

ABSTRACT

A gas turbine power plant is provided with an industrial gas turbine which drives a generator coupled to a power system through a breaker. The turbine-generator plant is operated by a hybrid control system having digital function capability during sequenced startup, synchronizing, load buildup and steady state load, and shutdown operations. The control system also contains monitoring and protective subsystems which function through all stages of operation, with redundancy and permissive features which maximize turbine availability.

CROSS-REFERENCE TO RELATED APPLICATIONS

U.S. patent application Ser. No. 319,114 filed by J. Reuther and T.Giras on Dec. 29, 1972 as a continuation of U.S. patent application Ser.No. 82,470 filed on Oct. 20, 1970 and now abandoned, entitled IMPROVEDSYSTEM AND METHOD FOR OPERATING INDUSTRIAL GAS TURBINE APPARATUS AND GASTURBINE ELECTRIC POWER PLANTS PREFERABLY WITH A DIGITAL COMPUTER CONTROLSYSTEM, and assigned to the present assignee.

U.S. patent application Ser. No. 323,593 filed by R. Yannone and R.Kiscaden on Jan. 15, 1973 as a continuation of U.S. patent applicationSer. No. 189,632 filed on Oct. 15, 1971 and now abandoned, entitledIMPROVED DIGITAL COMPUTER CONTROL SYSTEM AND METHOD FOR MONITORING ANDCONTROLLING OPERATION OF INDUSTRIAL GAS TURBINE APPARATUS TO DRIVESIMULTANEOUSLY AN ELECTRIC POWER PLANT GENERATOR AND PROVIDE EXHAUSTGASES TO AN INDUSTRIAL PROCESS, and assigned to the present assignee.

Reference is also made to the following co-filed and commonly assignedapplications, all filed by R. A. Yannone and J. J. Shields:

U.S. patent application Ser. No. 371,625 entitled GAS TURBINE POWERPLANT CONTROL APPARATUS HAVING A MULTIPLE BACKUP CONTROL SYSTEM;

U.S. patent application Ser. No. 371,626 entitled GAS TURBINE POWERPLANT CONTROL APPARATUS INCLUDING A SPEED/LOAD HOLD AND LOCK SYSTEM;

U.S. patent application Ser. No. 371,621 entitled GAS TURBINE POWERPLANT CONTROL APPARATUS INCLUDING AUTOMATIC LOAD PICKUP;

U.S. patent application Ser. No. 371,628 entitled GAS TURBINE POWERPLANT CONTROL APPARATUS INCLUDING AN AMBIENT TEMPERATURE RESPONSIVECONTROL SYSTEM;

U.S. patent application Ser. No. 371,627 entitled GAS TURBINE POWERPLANT CONTROL APPARATUS INCLUDING A TWO-SHOT SHUTDOWN SYSTEM;

U.S. patent application Ser. No. 371,623 entitled GAS TURBINE POWERPLANT CONTROL APPARATUS INCLUDING A TEMPERATURE RESET STARTING CONTROLSYSTEM AND AN IGNITION PRESSURE CONTROL SYSTEM;

U.S. patent application Ser. No. 371,630 entitled GAS TURBINE POWERPLANT CONTROL APPARATUS HAVING IMPROVED MONITORING AND ALARM ELEMENTS;and

U.S. patent application Ser. No. 371,624 entitled BEARING TEMPERATURESYSTEM FAILURE DETECTION APPARATUS SUITABLE FOR USE IN POWER PLANTS ANDLIKE APPARATUS.

BACKGROUND OF THE INVENTION

The present invention relates to gas or combustion turbine apparatus,gas turbine electric power plants and control systems and operatingmethods therefor.

Industrial gas turbines may have varied cycle, structural andaerodynamic designs for a wide variety of uses. For example, gasturbines may employ the simple, regenerative, steam injection orcombined cycle in driving an electric generator to produce electricpower. Further, in these varied uses the gas turbine may have one ormore shafts and many other rotor, casing, support and combustion systemstructural features which can vary relatively widely among differentlydesigned units. They may be aviation jet engines adapted for industrialservice as described for example in an ASME paper entitled "The Prattand Whitney Aircraft Jet Powered 121 MW Electrical Peaking Unit",presented at the New York Meeting in November-December 1964.

Other gas turbine uses include drive applications for pipeline orprocess industry compressors and surface transportation units. Anadditional application of gas turbines is that which involves recoveryof turbine exhaust heat energy in other apparatus such as electric poweror industrial boilers or other heat transfer apparatus. More generally,the gas turbine air flow path may form a part of an overall processsystem in which the gas turbine is used as an energy source in the flowpath.

Gas turbine electric power plants are usable in base load, mid-rangeload and peak load power system applications. Combined cycle plants arenormally usable for the base or mid-range applications while the powerplant which employs a gas turbine only as a generator drive, typicallyis highly useful for peak load generation because of its relatively lowinvestment cost. Although the heat rate for gas turbines is relativelyhigh in relation to steam turbines, the investment savings for peak loadapplication typically offsets the higher fuel cost factor. Anothereconomic advantage for gas turbines is that power generation capacitycan be added in relatively small blocks such as 25 MW or 50 MW, asneeded, for expected system growth thereby avoiding excessive capitalexpenditure and excessive system reserve requirements. Furtherbackground on peaking generation can be obtained in articles such as"Peaking Generation" a Special Report of Electric Light and Power datedNovember 1966.

Startup availability and low forced outage rates are particularlyimportant for peak load power plant applications of gas turbines. Thus,reliable gas turbine startup and standby operations are particularlyimportant for power system security and reliability.

In the operation of gas turbine apparatus and electric power plants,various kinds of controls have been employed. Relay-pneumatic typesystems form a large part of the prior art, but have heretofore notprovided the flexibility desired, particularly in terms of decisionmaking. Furthermore, such prior art systems have been characterized bybeing specially designed for a given turbine plant, and accordingly arenot adaptable to provide different optional features for the user. Morerecently, electronic controls of the analog type have been employed asperhaps represented by U.S. Pat. No. 3,520,133 entitled Gas TurbineControl System and issued on July 14, 1970 to A. Loft or by the controlreferred to in an article entitled Speedtronic Control, Protection andSequential System and designated as GER-2461 in the General Electric GasTurbine Reference Library. See also U.S. Pat. No. 3,662,545, whichdiscloses a particular type of analog acceleration control circuit for agas turbine; U.S. Pat. No. 3,340,883, relating to an analogacceleration, speed and load control system for a gas turbine. A widevariety of controls have been employed for aviation jet enginesincluding electronic and computer controls as described for example in aMarch 1968 ASME Paper presented by J. E. Bayati and R. M. Frazzini andentitled "Digatec (Digital Gas Turbine Engine Control), an April 1967paper in the Journal of the Royal Aeronautical Society authored by E. S.Eccles and entitled "The Use of a Digital Computer for On-Line Controlof a Jet Engine", or a July 1965 paper entitled " The Electronic Controlof Gas Turbine Engines" by A. Sadler, S. Tweedy and P. J. Colburn in theJuly 1967 Journal of the Royal Aeronautical Society. However, theoperational and control environment for jet engine operation differsconsiderably from that for industrial gas turbines.

The aforereferenced U.S. application W.E. 40,062, assigned to thepresent assignee, presents an improved system and method for operating agas turbine with a digital computer control system. In this system, oneor more turbine-generator plants are operated by a hybrid digitalcomputer control system, wherein logic macro instructions are employedin programming the computer for logic operations of the control system.

In referencing prior art publications or patents as background herein,no representation is made that the cited subject matter is the bestprior art.

While industrial gas turbine apparatus and gas turbine power plants haveattained a great sophistication, there remain certain operationallimitations in flexibility, response speed, accuracy and reliability.Further limits have been in the depth of operational control and in theefficiency or economy with which single or multiple units are placedunder operational control and management. Limits have existed on theeconomics of industrial gas turbine application and in particular on howclose industrial gas turbines can operate to the turbine design limitsover various speed and/or load ranges.

In gas turbine power plants, operational shortcomings have existed withrespect to plant availability and load control operations. Compressorsurge control response has been limited, particularly during startup.Temperature limit control has been less protective and less responsivethan otherwise desirable.

Generally, overall control loop arrangements and control systemembodiments of such arrangements for industrial gas turbines have beenless effective in operations control and systems protection than isdesirable. Performance shortcomings have also persisted in theinterfacing of control loop arrangements with sequencing controls.

With respect to industrial gas turbine startup, turbine operating lifehas been unnecessarily limited by conventional startup schemes.Sequencing systems have typically interacted with startup controls lesseffectively than desirable from the standpoint of turbine and powerplant availability. More generally, sequencing systems have provided forsystematic and protective advance of the industrial gas turbineoperations through startup, run and shutdown, but in doing so have beenless efficient and effective from a protection and performancestandpoint than is desirable.

Restrictions have been placed on operations and apparatus managementparticularly in gas turbine power plants in the areas of maintenance andplant information acquisition. Further management limits have existedwith respect to plant interfacing with other power system points,operator panel functionality, and the ability to determine plantoperations through control system calibration and parameter changes.

The computerized gas turbine control as disclosed in W.E. applicationSer. No. 319,114 has been highly successful in providing controlcapability and flexibility of control options that had not previouslybeen incorporated into an all hardware type system. However, while thecomputerized, or software control system provides substantial advantagesdue to its logic performing capability, historical data storage anddiagnostic programs, it also has a number of shortcomings. The interfacebetween the turbine and its associated analog signals and the computercontroller presents areas for future development and improvement. Theanalog input system is a complex multiplexing arrangement requiringsharing of the scan time by the variables which must be scanned or read"independently". In the system disclosed, there is a scanning rate of 30per second, meaning that 30 input variables per second can be read,imposing a limitation on the ability of the system to respond rapidly toa given input variable when program running time is also added to thedelay. In addition, the computer system itself incorporates elaboratetechniques of self-diagnosis of failure, which can result in turbineshutdowns when the computer has determined that something has failedwithin the central processor, input-output, or peripheral hardware. Itis most difficult for the computer to determine whether the failure isof a sufficiently critical nature to require shutdown. In fact, it hasbeen found that failures in the analog input-output system may not bereadily differentiated, leaving the computer no choice but to shut downthe entire turbine system for a failure which may not justify loss ofload availability. Since all monitoring and protection paths arechanneled through a central processor, a self-determination of failurein the central processor, analog input multiplexing or output system bythe computer controller necessitates blocking off all channels, suchthat complete system shutdown is required. Furthermore, even duringnormal operation, the computerized system provides low visibility withrespect to the health of the control system. The essential intermixingof the control paths through the central processor makes it difficultfor the operator to obtain information as to the mode of control at anymoment, or to obtain quantitative information as to the relativemagnitudes of the different control signals. In short, the increasedflexibility of the software system is achieved at the expense ofoperator visibility such as permits optimum maintenance procedures.Accordingly, there is a great need in the art for a turbine systemhaving a control with the logic capability of a digital system, butretaining the advantages which are inherent in simpler designs.

The gas turbine control system as disclosed herein incorporates novelfeatures which are specifically designed to meet the above generalrequirements, and which go further in providing operating capability notheretofore available in any turbine control system. The control systemof this invention includes a plurality of continuously closed controlloops, each of which continuously generates a control signal adapted tocontrol the turbine fuel system, and thereby control available fuel tothe turbine, thereby controlling turbine operation itself. Each of thecontrol loops contains logic capability, is adaptable to be constructedin different hardware forms, and provides continuous visual indicationfor the operator and continuous monitoring for alarm or turbineshutdown. In this manner, should failure, or even a lesser malfunction,occur in any of the control paths, a backup control signal is availableto take over turbine control, without the failure causing loss ofturbine availability. Furthermore, means are provided by which theoperator can immediately determine the source and, in many instances,the nature of the malfunction, so that corrective maintenance can bequickly and efficiently undertaken.

Another specific improvement is the provision of adapting the turbinecontrol for changes in ambient temperature, such as occur between summerand winter operation. In prior art systems, which are dependent solelyon monitoring of internal turbine conditions, unwanted operatinglimitations are imposed by changes in ambient temperature. Suchlimitations have been reduced substantially by the novel adaptivecontrol means disclosed herein.

Another area of great importance in gas turbine control is that ofimmediately meeting load demand upon generator breaker closing. Pastcontrols have generally provided for a continuous buildup of load,starting from zero load at generator breaker closing and proceedingroughly linearly to a desired load level. However, there are a number ofapplications where it is required, or at least highly desirable, toprovide an essentially instantaneous pickup of load. Accordingly, thisinvention provides novel means for controlling the turbine fuel flow soas to provide capability for such immediate load pickup.

A critical portion of the operation of any turbine involves the startingsequence, at which time the turbine undergoes severe temperaturechanges, with possible resulting damage due to thermal stress. Theturbine control system of this invention accordingly incorporates novelfeatures to limit turbine speed change as a function of monitoredturbine temperature, and to schedule the fuel supplied to the turbinecombustor element so as to minimize risk of thermal damage during thestarting operation. One of the novel techniques employed in this respectis the specific means of scheduling bypass fuel flow in the turbine fuelsystem during startup, so as to control the fuel pressure at thecombustor nozzles. A bypass temperature limiter valve suitable in thisoperation, with which desired combustor nozzle fuel pressure is obtainedduring ignition, is disclosed in co-pending U.S. patent application Ser.No. 261,192, assigned to the same assignee. The technique disclosedherein involves novel means of utilizing apparatus such as is disclosedin Ser. No. 261,192.

One of the greatest needs in any turbine control system is that ofproviding operator flexibility, and in particular providing the operatorwith the capability of efficiently changing load as desired. Most priorart turbine control systems are quite limited in the degree offlexibility available to the operator, e.g., only discrete operatingload levels are available, or the available means of changing the loadlevel to a desired level is cumbersome and/or cannot be achieved at adesired rate. Accordingly, the control system of this invention providesnovel means having essentially unlimited flexibility for operator changeof the load level, rate of change of such load level, the ability tohold load at any desired level, and the ability to return to anypredetermined load level. This capability is constantly backed up bytemperature control capability, such that no matter what the operatorattempts to do, operational limits are automatically imposed as afunction of sensed turbine temperatures.

A yet further need in a turbine control system is that of providing areliable and workable monitoring system. As pointed out hereinabove, incomputerized turbine control systems all monitoring and protection pathsare channeled through a central processor, which frequently results inthe computer requiring complete shutdown when, in fact, the turbine isbeing operated within safe limits. Also, even during normal operation,the computerized system frequently does not permit the degree ofmonitoring visibility which is highly advantageous for providing theoperator with optimum ability to oversee the turbine operation. In orderto overcome these difficulties and provide improved visibility andreliability, while maintaining maximum turbine availability, there is aneed for a control system designed so as to provide continuous visualindication as to the current mode of turbine control, so that theoperator can determine the health of the control system. This may beachieved by providing discrete modularized control paths which are inconstant communication with the turbine and which generate independentcontrol signals, and means for determining and displaying which of saidindependent signals is at any given moment in control of the turbineoperation.

Turbine availability may also be greatly enhanced by providing means forautomatically restarting the turbine after an automatic shutdown, upon adetermination that safe conditions exist for such restarting. In manycases, the condition which caused the turbine to be placed in shutdownis corrected, or corrects itself, shortly after shutdown is initiated.However, in conventional turbine control systems, the turbine must bebrought substantially completely to the shutdown state, and thenrestarted all over again. It is clear that this results in avoidableloss of turbine availability, and that there is a need to minimize theloss of availability by restarting as soon as turbine conditions permit.The gas turbine monitoring system as disclosed herein provides ashutdown subsystem having a novel arrangement for automaticallyrestarting the turbine after correction of the malfunction which causedshutdown.

The monitoring system of this invention also incorporates a uniquesystem and method for optimizing load availability while providing analarm or other means to alert the operator to the existence of a controlmalfunction which must be corrected but which does not merit immediateturbine shutdown. This unique system avoids the inflexibility ofcurrently used monitoring circuits which are designed either to befail-safe (in which case load availability is sacrificed to ensureshutdown), or which are designed to fail in a designated direction,(thus always providing continuing availability, but at the cost of notshutting down in instances where shutdown might be required).

SUMMARY OF THE INVENTION

An industrial gas turbine or gas turbine-generator power plant isoperated by a hybrid control system which is particularly adapted tooptimize interfacing of control loops, sequencing controls andmonitoring functions, so as to maximize turbine availability. Thecontrol system operates in a gas turbine control loop arrangement tocontrol fuel flow and thereby provide speed, load and loading ratecontrol over the turbine, and also to provide backup temperature limitcontrol. The control paths have independent input interfaces with theturbine, and further provide, along with the monitoring subsystem, highreliability through redundancy and multiplicity features.

There is provided a gas turbine electric power plant having a controlsystem for controlling the load deliverable by the power plantgenerator, with the ability to select the rate at which load is changed,and with continuous temperature backup control of the turbine operation.Accordingly, a gas turbine electric power plant with a load controlsystem for controlling the load supplied by the gas turbine is utilized,having means for generating at least two control signals adaptable tocontrol turbine load according to respective predetermined schedules,means for selecting the rate of change of at least one of said loadcontrol signals, means for providing a temperature limiting signal, andmeans for selecting one of such load control signals as a primary signalfor controlling load level. The selection means may be automatic oroperator controlled, providing operator flexibility in achieving desiredload levels, all while having temperature backup control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top plan view of a gas turbine power plant arranged tooperate in accordance with the principles of the invention.

FIG. 2 shows a front elevational view of an industrial gas turbineemployed in the power plant to drive a generator and is shown with someportions thereof broken away.

FIG. 3 shows portions of the ignition system apparatus used in theturbine of FIG. 2.

FIG. 4 shows a block diagram of the electro-pneumatic fuel flow systemfor the gas turbine of FIG. 2.

FIG. 5 shows a block diagram of the control paths for generating theprimary control signal for controlling speed and load of the turbine ofFIG. 2.

FIG. 6A shows a schematic diagram of the temperature control paths ofthe electro-pneumatic control system for the turbine of FIG. 2.

FIG. 6B shows temperature-P_(2C) curves for different load modes for theturbine of FIG. 2.

FIG. 6C shows a diagram of the manner in which the operating parametersof the turbine are modified as a function of ambient temperature.

FIG. 7A shows a schematic diagram of the speed and load control paths ofthe electro-pneumatic control system for the turbine of FIG. 2.

FIG. 7B illustrates the manner in which the control system of thisinvention enables a step load pickup at generator closing.

FIG. 8A shows a block diagram of the fuel starter control systememployed to generate starting signals for the turbine of FIG. 2.

FIG. 8B shows a block diagram of the manner in which the startingsignals are used to control fuel flow to the turbine of FIG. 2.

FIG. 8C shows a circuit diagram of an electronic embodiment of thesequence control portion of the novel ignition pressure controlsubsystem of this invention.

FIG. 8D shows a schematic diagram of the pneumatic embodiment of theignition pressure control subsystem of this invention.

FIG. 8E shows curves depicting the operation of the ignition pressurecontrol subsystem of this invention.

FIG. 9 shows typical start curves for the turbine.

FIG. 10 shows typical loading curves for the turbine.

FIG. 11 shows a schematic diagram of a portion of the speed controlcircuitry of the control system for the turbine.

FIG. 12 shows a schematic diagram of a portion of the load controlcircuitry of the control system for the turbine.

FIG. 13 shows a schematic diagram of the electrical circuitry forselection of the mode of load control.

FIG. 14A shows a schematic diagram of the "2-shot" circuitry associatedwith the turbine protective portion for protecting the turbine.

FIG. 14B shows a first block diagram of the logic functions of the2-shot protective system.

FIG. 14C shows a second block diagram of the logic functions of the2-shot protective system. FIG. 14D illustrates a start-up sequenceutilizing the 2-shot protective system.

FIG. 15 shows a block diagram of a portion of the control system foroperating the turbine in the minimum load mode.

FIG. 16 shows a block diagram of the control system for operating theturbine in the base load mode.

FIG. 17 shows a block diagram of a portion of the control system foroperating the turbine in the peak load mode.

FIG. 18 shows a block diagram of the control system for operating theturbine in the system reserve mode.

FIG. 19 shows a block diagram of a portion of the control system foroperating the turbine in the fast load mode.

FIG. 20 shows a block diagram of a portion of the control system foroperating the turbine in the starting fuel control mode.

FIG. 21 shows a block diagram of a portion of the control system foroperating the turbine in the manual load mode.

FIG. 22A shows a first portion of a schematic diagram of the circuitryfor the speed/load hold and lock subsystem.

FIG. 22B shows a second portion of a schematic diagram of the circuitryfor the speed/load hold and lock subsystem.

FIG. 23A shows a schematic diagram of an embodiment of the turbinecontrol system of this invention having both closed loop "load" controland closed loop "speed" control.

FIG. 23B shows a modification of the embodiment of FIG. 23A, adapted tobe used with the speed/hold load and lock subsystem of FIGS. 22A and22B.

FIG. 24 shows a schematic diagram of the master relay portion of theprotection portion of the electro-hydraulic control system of thisinvention, and a first portion of the circuitry for controlling theignition sequence.

FIG. 25 shows a schematic diagram of a further portion of the ignitionsequence circuitry.

FIG. 26A shows a representation of the operating ranges of athermocouple used in the novel protection circuit of this invention.

FIG. 26B shows a schematic diagram of the novel alarm/failure protectioncircuit of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A. POWER PLANT 1. GeneralStructure

Referring now to FIG. 1, there is shown a gas turbine electric powerplant 100 which includes an AC generator 102 driven by a combustion orgas turbine 104 through a reduction gear unit 27. In this application ofthe invention, the gas turbine 104 may be the W-251G simple cycle typemanufactured by Westinghouse Electric Corporation. In other power plantgenerator applications, other industrial drive applications, andcombined steam and gas cycle applications of various aspects of theinvention, industrial gas turbines having larger or smaller powerratings, different cycle designs, or a different number of shafts thanthe W-251G can be employed.

The plant 100 may be housed in an enclosure (not shown) and then placedon a foundation approximately 106 to 115 feet long dependent upon thenumber of optional additional plant units to be accommodated thereon.Three or more additional units may be provided. Exhaust silencers 29 and36, coupled respectively to inlet and exhaust duct works 31 and 38,significantly reduce noise characteristicly associated with turbinepower plants.

Startup or cranking power for the plant 100 is provided by a startingengine 26, such as a diesel engine. Starting engine 26 is mounted on anauxiliary bedplate and coupled to the drive shaft of the gas turbine 104through a starting gear unit 28. A DC motor 54 operates through aturning gear 56 which is also coupled to the gas turbine shaft startinggear 28 to drive the gas turbine at turning gear speed.

A motor control center 30 is also mounted on the auxiliary bedplate andit includes motor starters and other devices to provide for operatingthe various auxiliary equipment items associated with the plant 100.

A plant battery 32 is disposed adjacent to one end of the auxiliarybedplate or skid. The battery provides power for emergency lighting,auxiliary motor loads, and other control power for a period followingshutdown of the plant 100 due to a loss of AC power. The battery alsosupplies power for the DC lube pump, DC turning gear, DC/AC inverter,and is available for block plant starting. Also included on theauxiliary skid is pressure switch and gauge cabinet 55 which containsthe pressure switches, gauges, regulators and other miscellaneouselements needed for gas turbine operation.

A switchgear pad 42 is included in the plant 100 for switchgearincluding the generator breaker as indicated by the reference characters44, 46 and 48. Excitation switchgear 50 associated with the generatorexcitation system is also included on the switchgear pad 42.

2. Gas Turbine a. Compressor

The gas turbine 104 is suitably of the single shaft simple cycle typehaving a standard ambient pressure ratio of 9.0 to 1 and a rated speedof 4894 rpm, and is illustrated in greater detail in FIG. 2. Filteredinlet air enters a multistage axial flow compressor 81 through a flangedinlet manifold 83 from the inlet ductwork 31. An inlet guide vaneassembly 82 includes vanes supported across the compressor inlet set atan optimum position for controlling machine airflow. The angle at whichall of the guide vanes are disposed in relation to the gas stream isuniform and mechanically fixed by a positioning ring coupled to thevanes in the inlet guide vane assembly 82.

The compressor 81 is provided with a casing 84 which is split into baseand cover parts along a horizontal plane. The turbine casing structureincluding the compressor casing 84 provides support for a turbinerotating element including a compressor rotor 86 through bearings 88 and89. Vibration transducers (not shown) are provided for these two maingas turbine bearings 88 and 89.

The compressor casing 84 also supports stationary blades 90 insuccessive stationary blade rows along the air flow path. Further, thecasing 84 operates as a pressure vessel to contain the air flow as itundergoes compression. Bleed flow is obtained under valve control fromintermediate compressor stages to prevent surge during startup.

The compressor inlet air flows annularly through a total of eighteenstages in the compressor 81. Blades 92 mounted on the rotor 86 by meansof wheels 94 are appropriately designed from an aerodynamic andstructural standpoint for the intended service. A suitable material suchas 12% chrome steel is employed for the rotor blades 92. Both thecompressor inlet and output air temperatures are measured by suitablysupported thermocouples.

b. Combustion System

Pressurized compressor outlet air is directed into a combustion system96 comprising a total of eight combustor baskets 98 conically mountedwithin a section 80 of the casing 84 about the longitudinal axis of thegas turbine 104. Combustor shell pressure is detected by a suitablesensor (not shown) which is coupled to the compressor-combustor flowpaths and is located in the pressure switch and gauge cabinet 55.

As schematically illustrated in FIG. 3, the combustor baskets 98 arecross-connected by cross-flame tubes 302 for ignition purposes. Ignitionsystem 304 includes igniters 306 and 308 associated with respectivegroups of four combustor baskets 98. In each basket group, the combustorbaskets 98 are series cross-connected and the two groups arecross-connected at one end only as indicated by the reference character310.

Generally, the ignition system 304 includes an ignition transformer andwiring to respective spark plugs which form a part of the igniters 306and 308. The spark plugs are mounted on retractable pistons within theigniters 306 and 308 so that the plugs can be withdrawn from thecombustion zone after ignition has been executed. The spark plugswithdraw automatically as compressor discharge pressure increases.

A pair of ultraviolet flame detectors 312 are located in each of the twoend combustor baskets in the respective basket groups in order to verifyignition and continued presence of combustion in the eight combustorbaskets 98. The flame detectors 312 can for example be Edison flamedetectors Model 424-10433.

c. Fuel

Generally, either liquid or gaseous or both liquid and gaseous fuel flowcan be used in the turbine combustion process. Various gaseous fuels canbe burned including gases ranging from blast furnace gas having low BTUcontent to gases with high BTU content such as natural gas, butane orpropane.

With respect to liquid fuels, the fuel viscosity must be less than 100SSU at the nozzle to assure proper atomization. Most distillates meetthis requirement. Heavier fuels must be heated.

A portion of the compressor outlet air flow combines with the fuel ineach combustor basket 98 to produce combustion after ignition and thebalance of the compressor outlet air flow combines with the combustionproducts for flow through the combustor basket 98 into a multistagereaction type turbine 34 (FIG. 2). The combustor casing section 80 iscoupled to a turbine casing 85 through a vertical casing joint 87.

d. Turbine Element

The turbine element 34 (FIG. 2) is provided with three reaction stagesthrough which the multiple stream combustion system outlet gas flow isdirected in an annular flow pattern to transform the kinetic energy ofthe heated, pressurized gas into turbine rotation, i.e., to drive thecompressor 81 and the generator 102. The turbine rotor is formed by astub shaft 39 and three disc blade assemblies 41, 43 and 45 mounted onthe stub shaft by through bolts.

High temperature alloy rotor blades 51 are mounted on the discs informing the disc assemblies 41, 43 and 45. Individual blade roots arecooled by air extracted from the outlet of the compressor 81 and passedthrough a coolant system in the manner previously indicated. The bladeroots thus serve as a heat sink for the rotating blades 51. Cooling airalso flows over each of the turbine discs to provide a relativelyconstant low metal temperature over the unit operating load range.Thermocouples (not shown) are supported within the cooled disc cavitiesto provide cavity temperature signals for the control system. Theperformance of the cooling air flow is detected by these thermocouples.

In addition to acting as a pressure containment vessel for the turbineelement 34, turbine casing 85 supports stationary blades 49 which formthree stationary blade rows interspersed between the rotor blade rows.Gas flow is discharged from the turbine element 34 substantially atatmospheric pressure through turbine cylinder 53 to exhaust manifold 38.

The generator and gas turbine vibration transducers can be conventionalvelocity transducers or pickups which transmit basic vibration signalsto a vibration monitor for input to the control system. A pair ofconventional speed detectors 78 (FIG. 4) are associated with a notchedmagnetic wheel supported at appropriate turbine-generator shaftlocations. Signals generated by the speed detectors are employed in thecontrol system for speed control and speed monitoring.

Further, thermocouples 180 (FIG. 4) for the blade path are supportedabout the inner periphery of the turbine cylinder 53 to provide a fastresponse indication of blade temperature for control system usageparticularly during plant startup periods. Exhaust temperature detectors57 are disposed in the exhaust manifold 38 primarily for the purpose ofdetermining average exhaust temperature for control system usage duringload operations of the power plant 100. Suitable high response shieldedthermocouples for the gas turbine 104 are those which use compactedalumina insulation with a thin-wall high alloy swaged sheath or wellsupported by a separate heavy wall guide.

B. TURBINE FUEL CONTROL SUBSYSTEM

Referring now to FIG. 4, there is illustrated a detailed block diagramof the electro-pneumatic system of this invention employed to controlliquid fuel flow for the gas turbine power plant of FIG. 1. An exciter33 is shown connected to a generator 102, which is coupled to theturbine through reduction gear unit 27. A main lube pump 35 is alsodriven from unit 27, to provide pressure for the turbine oil system. Theturbine unit is shown in diagrammatic form as comprising compressor 81,combustion system 96 (having 8 baskets) and turbine element 34. Startingengine 26 is coupled to the turbine through starting gear unit 28 as isturning gear 56. A pressure representative of the ambient temperature atcompressor 81 is developed by transmitter 71. Pressure switch 70provides a signal when ignition speed is reached in the compressor.Similarly, thermocouple system 180, also comprising two groups ofthermocouples, is positioned in turbine element 34 to provide a signalrepresentative of blade path temperature, and thermocouple system 57provides a signal representative of turbine exhaust temperature.

The liquid fuel system is powered by main fuel pump 40, (driven fromreduction gear unit 27) which draws fuel from supply 93. Pump 40 isoperative unless deenergized by pneumatic overspeed trip mechanism andvalve 91, and is limited by relief valve 105 connected across pump 40.Trip valve 91 is powered by a pneumatic autostop trip signal derivedfrom a trip pressure system (not shown) and functions to prevent fuelfrom reaching the combustors at overspeed. The trip valve 91 is set totrip at 1.1 times synchronous speed.

From main pump 40, the fuel flows through normally open overspeed fueltrip valve 103, throttle valve 99, and fuel oil isolation valve 101 toconventional fuel distributor 107, which distributes the fuel to thevarious combustion baskets 98 of combustion system 96. Trip valve 103 isnormally open, permitting fuel flow to the distributor, but closes toshut off fuel flow upon sensing a drop in pressure which occurs onoperation of the overspeed trip valve 91 (or upon operation of a manualtrip valve, not shown). Isolation valve 101 is opened when pressure inthe overspeed trip system is detected to equal at least 40 psi at whichtime solenoid valve 108 is energized, permitting passage of actuatingair through to valve 101.

Fuel throttle valve 99 is positioned by the fuel throttle valve signalcommunicated thereto through throttle solenoid 119 which is energized atignition (as described in more detail hereinbelow). The throttle valveis shunted by a pressure-temperature (PT) limiter valve 109 as well aspump discharge valve 97. The PT valve is actuated by air from theisolation valve air system, such that when isolation valve solenoid 108is energized, the PT valve is positioned to a fixed opening providing alimiting function at ignition. Pump discharge valve 97 is positioned bya fuel starting signal as described hereinafter, such that it controls aconstant fuel pump discharge pressure from 50% speed to full load afterfirst ramping pressure from the Ignition-20% speed condition.

The turbine system of this invention also contains a parallel gas fuelsystem, not illustrated in detail in the drawings. The gas fuel systemalso similarly interposes an auto stop trip valve, a throttle valve andan isolation valve between the gas supply and the turbine combustionsystem. A starting valve, having a positioner actuated by the startingsignal as described hereinbelow, shunts the throttle valve.

FIG. 4 also indicates a number of sensing devices which provideimportant inputs to the turbine control system. A pressure switch 70 isactivated when compressor pressure reaches a value corresponding toignition speed. An ambient temperature transmitter 71 produces a signalrepresentative of the ambient temperature into the compressor inlet.Exhaust thermocouples 57 monitor the turbine exhaust temperature, andblade path (B/P) thermocouples 180 monitor the blade path temperature.Speed sensors 78 provide a signal representative of the turbine speed.

C. GAS TURBINE MULTIPLE BACKUP CONTROL SYSTEM a. General Description

The preferred form of the apparatus of this invention for gas turbinespeed and load control utilizes electro-pneumatic control componentsarranged in a manner so as to carry out digital computer-type logicfunctions with the reliability of special-purpose hardware. Theoperational sequence is accomplished by conventional control relays,with a combination of electro-pneumatic fuel scheduling, and is combinedwith an all solid state protective monitoring system. The control systemfeatures permissible manual local control, while being designed forcompletely automatic fully remote control. Areas of critical controloperation such as starting temperature control, loading temperaturecontrol and speed control are supplied with total redundancy to permitcontinued operation upon failure of one section, and generous indicationof fuel control modes is provided by light indication for ease ofoperation and maintenance.

Six control channels are used, namely load, speed-load, acceleration(surge), load-rate, exhaust temperature and blade path temperature.Speed control is effectuated through a pneumatic speed changer withbackup control from both the acceleration channel and the blade pathchannel. Primary load control is achieved through a pneumatic loadscheduler with backup temperature control from the blade path channel(for transient control) and from the exhaust temperature channel (forsteady state control). When acting as a backup to speed control, theblade path channel produces a signal which is a function both ofcompressor discharge pressure and ambient temperature. During loading,the signals of both the blade path and exhaust temperature channels arereferenced to a common compressor discharge pressure signal biased inaccordance with the chosen load mode.

The output signals generated in each of the six control channels areprovided as inputs to a low pressure selector, a pneumatic device whichgates through to its output the lowest of its pneumatic inputs. Theoutput of the low pressure selector (LPS) is supplied to a fuel gasvalve servo control or to a fuel oil valve servo control, depending uponthe selection of fuel. The lift of the fuel throttle valve (either oilor gas) is proportional to the output pressure of the LPS. When suchoutput pressure is 3 PSI (or 1 volt, for analog system), or less, thethrottle valve is at minimum lift position, and the turbine is undercontrol of the PT or Pump Discharge Pressure Control Valves. When theLPS output exceeds about 3 PSI or 1 volt (about 50% speed) the throttlevalves begin to open, and open proportionately up to a maximum liftposition, corresponding to a signal of about 15 PSI (or 10 voltsanalog).

The exhaust temperature control is the normal controlling mode underload conditions. In the exhaust temperature control loop, the setpointis obtained from a signal proportional to the compressor dischargepressure (a function of ambient temperature and compressor performance),and biased variously for either base load operation, peak loadoperation, or system reserve operation. Thus, these three modes of loadoperation are temperature-control modes. Each of these modes requires aspecific fuel flow for a definite average temperature at the turbineinlet. Due to the high level of this temperature, it is not practical tomeasure a representative turbine inlet temperature, and therefore theexhaust temperature is measured and is used to calculate the inlettemperature. The exhaust temperature loop utilizes a PID (proportional,integral and derivative action) controller to generate the controlsignal (a function of both exhaust temperature and compressor dischargepressure). The exhaust temperature is sensed by 16 thermocouples,averaged in two groups of eight thermocouples each. The electricalsignals from these two groups are transduced to pneumatic signals (oramplified in the analog embodiment), and a high (pressure) selector isutilized to select the higher value to prevent shutdown when pressurefailure occurs at the output of one of the transducers. Thismultiplicity feature is exemplary of the manner in which this systemprovides improved reliability and load availability. The high (pressure)selector output is connected to a direct derivative device whichfunctions to speed up the exhaust temperature control system. Theexhaust thermocouples react slower to turbine temperature changes due totheir downstream location, and the derivative device compensates forthis slower response.

The blade path temperature control is used as backup for the exhaustcontrol. For this reason, the blade path pneumatic controller is biasedslightly higher than that of the exhaust temperature controller, whilereceiving the same setpoint pressure under load control operations.During starting, the blade path controller receives its reference signalfrom a compressor discharge pressure signal which is biased by anambient temperature signal, to provide a blade path control signalusable as backup control during the starting sequence.

Another unique feature of the reliability by multiplicity isdemonstrated in the event of the unlikely loss of the total redundantexhaust measuring system. The blade path starting temperature control isrebiased to pick up this function whiile alarming and continuing tosupply power in the run position.

Besides the fuel scheduling system, reliability by multiplicity islikewise inherent in the turbine protective system. The speed control,exhaust and blade path temperature system, disc cavity and bearingprotection, as well as the ignition, flame, and vibration systems, all,by the way they are designed, embody "load availability". If componentsor portions of these systems fail, the design criteria embodied in thisinvention provides that the turbine continue producing power by alarmingthe condition, but selectively auctioneering the need to cause turbineshutdown. This is in marked contrast to computer-controlled systems, aswell as prior art analog controlled systems.

Although some redundancy, where feasible and effective, is used toaccomplish the Perpetual Power Production ("PPP") objective, duplicationof components is not the only means for accomplishing this goal. Thebearing monitoring system employs a unique means of detecting openthermocouples while the machine is running, and at the same time,causing a shutdown if a hot bearing warrants this action. The disccavity monitoring system requires 2 alarms in the same cavity to producea shutdown, based upon the premise that 2 open thermocouples in the samecavity at the same time are unlikely. Since the turbine system will shutdown on a high exhaust or blade path temperature average, openthermocouples can do little more than change the non-controllingaverage. Also, failure of one side of the loop results in an automaticshift to the other side and an alarm display to notify the operator.This is likewise a feature of the vibration systems, where a pickupfailure is alarmed while the turbine continues to run.

The speed system is unique in that dual pickups, dual channels, andauctioneering circuits are provided to alarm outage greater than 5%. Thespeed system continues running by selecting the higher of twoinputs--once again based on the design premise that high readings underfailure are unlikely.

In addition, as is discussed hereinbelow in relation to the specificembodiments, the system of this invention utilizes a modularity conceptfor functions and hardware employed to obtain reliability bymultiplicity. Each control function, and each corresponding hardwareportion, may be either pneumatic, analog or digital, or a hybridcombination. In contrast to prior art systems where hardware ismultiplexed to accomplish functions, each control loop is independentand not time shared. The failure of one function or component in thesystem does not cause starting to abort or turbine to shut down. As aresult, no local additional maintenance control system is necessarysince the system has self-contained back-up control.

In the detailed description of the electropneumatic embodiment whichfollows, only those elements important for an understanding of thesystem are illustrated. However, it is recognized that the total systemcomprises a number of additional elements which are necessary componentsof the entire system. The following is a partial list of such backupelements, which are not illustrated in the drawings:

a. Turbine cooling air system. This system provides cooling air to theturbine blading and disc cavities and for the rotor cooling.

b. Atomizing air system. When oil fuel is used an atomizing device isrequired to break up and atomize the fuel oil into minute particles toobtain maximum combustion of the fuel mixture during the ignitionperiod.

c. Instrument air system. This system consists of an independentcompressor, reservoir filters and several control devices. Theindependent compressor functions only during initial starting, and at alower capacity after shutdown. When the turbine compressor pressure issufficient, the independent compressor is shut off and the turbinecompressor supplies the instrument air. The instrument air systemprovides the required air supply for all of the pneumatic devicesillustrated as components of the control system. In the discussion tofollow, air pressures are recited as being PSI, although such pressuresare in fact gauge pressures.

The specific pneumatic devices which are discussed in detail hereinbeloware all commercially available devices, and no claim is made as to thenovelty of any such pneumatic devices. The controllers, transmitters,pilot relays, reducing relays, amplifying relays, direct derivativeunits, low pressure selector, high pressure selectors, high limitrelays, bias relays, and totalizing relays are all available from MooreProducts Co., Springhouse, Pa. See, for example, the Moore publicationtitled "Nullmatic Controllers", Bulletin 5018, which describes in detailthe pneumatic controllers as specified hereinbelow.

b. Detailed Description

Referring now to FIG. 5, there is shown a block diagram of the controlpaths for generating, from different inputs, control signals suitablefor control of turbine fuel flow, and consequently of turbine speed andload. In the embodiment as illustrated by this block diagram, eachcontrol path develops a pneumatic signal, and the plurality of pneumaticsignals thus developed are connected to a low pressure select element231, which selects that signal having the lowest pressure and producesit as the output control signal. While the system as thus illustrated inFIG. 4 is primarily pneumatic, it is to be understood that the samefunctions may be performed with equivalent analog or digital means.

The turbine combustor shell pressure (compressor discharge pressure)P_(2C) is communicated from the turbine combustion system 96 and isoperated upon, as shown in block 250, to produce a pneumatic pressurewhich is a function of P_(2C). Also communicated to block 250 isinformation concerning whether the turbine is being operated in thebase, peak or system reserve load mode, and the operation at block 250produces an output which is a different function of P_(2C) dependingupon the chosen mode. As seen in FIG. 6B, the T_(2T) -P_(2C) curvevaries as a function of the load level carried by the turbine, whereT_(2T) represents B/P or EXH temperature. The output from 250 isconnected to block 203. Also connected to block 203 is a pressure signalfrom block 251 representing a function of the exhaust temperature asmeasured by thermocouples positioned at the turbine exhaust location.The operation at block 203 comprises proportional, integral andderivative action to produce an output signal which is a function of themeasured exhaust temperature as compared to the setpoint as produced bythe output of block 250. The signal from block 203 thus represents aconstraint on exhaust temperature as a function of shell pressure, inaccordance with the known relationship between these two variables (asillustrated in FIG. 6B). The output of block 203, designated EXH, isconnected to the input of the low pressure select block 231.

A second control path is employed to derive a control signal which is afunction of the blade path temperature. As shown at block 258, the bladepath temperature is determined from thermocouples placed in the bladepath, and such determined temperature is converted into an appropriatepressure which is a function of blade path temperature, T_(2T). Inaddition, the combustor shell pressure P_(2C) is converted into acorresponding pressure at block 252 and the ambient temperature issensed and converted to a respective corresponding pressure at block253. These two pressures are totaled at block 190, to give an outputpressure representative of the algebraic sum of such two inputpressures. The signal from block 258 is connected to block 204 as aninput variable signal, and the signal from block 190 is connected as asetpoint signal, and both are operated on at block 204 by proportionaland integral action to develop the blade path (B/P) signal, comprisingthe second input to block 231.

The third control path comprises totaling, at 209, the P_(2C) signal aswell as a bleed path (B/V) signal representative of turbine surge. Theoutput of this totaling step produces an acceleration limit signal.

A fourth control path, designated speed load, produces a signal which isa function of sensed speed as compared to a variable speed setpoint. Asshown at block 260, speed is sensed by appropriate sensors, andconverted to a pressure signal representative of such speed, whichpressure signal is introduced at block 205 as a variable input. Avariable speed setpoint is produced by a speed changer 65S, which in thepreferred embodiment is a pneumatic generator. The speed changer output,designed to accelerate the turbine from 50% speed to 100% speed, isintroduced to block 205 as the setpoint. A signal is developed at block205 proportional to the difference between the setpoint and thevariable, and is communicated to block 231 as the speed load signal.

A fifth control path produces a load signal, and comprises generating aprogrammable signal at load changer block 65L, the output of which maybe modified at block 65-FN to produce a fast changing or normal changingload signal, the output of block 65-FN in turn being connected to theselect block 231. In addition, a sixth variable control signal isgenerated at block 188, which has as its input the output of the lowsignal select block 231, and produces an output which limits the limitor rate of change of the control signal.

At block 231, the six inputs are compared and the low value is chosenand gated through to the output at terminal T231. This signal isemployed to control the throttle valve, or valves, which in turn controlthe amount of fuel being delivered to the turbine combustors. For normaloperation, the exhaust and B/P signals, which are temperature controlsignals, are biased higher than the speed and load signals, so thatduring normal trouble-free operation, they do not control. However,these control signals are present as backup control, and in thepreferred embodiment of the invention at all times during operation ofthe turbine, system temperature backup control is available.

Referring now to FIG. 6A, there is illustrated a schematic diagram ofthe temperature control paths of the control system of this invention.As discussed with respect to the basic control block diagram of FIG. 5,the backup temperature control signals are generated as a function ofcompressor discharge pressure P_(2C) and the corresponding measuredcontrol temperature. P_(2C), obtained at the combustor as illustrated inFIG. 4, is connected to the pressure switch 153, and thence totransmitters 207 and 208, each of which provide pneumatic signalsrepresentative of P_(2C). The signal from transmitter 208 is in therange of 3 to 15 PSI and is coupled to the inputs of bias relays 158 and152 respectively, as well as a first input to solenoid valve 137. Biasrelay 152 biases the signal from 208 with about 2 PSI which signal isthen connected to a first input of solenoid operated valve 136. Biasrelay 158 biases the signal from transmitter 208 with about 1 PSI, whichsignal is then connected to a second input to valve 137. The output ofvalve 137 is connected to a second input to valve 136, and the output ofvalve 136 is communicated to input R of exhaust controller 203. Theexhaust temperature controller 203 is a proportional, integral andderivative action controller having direct controller action such thatthe output at CO varies directly with the input at C. The input signalto controller 203 is derived from 16 thermocouples, averaged in twogroups of 8 thermocouples each, indicated at 57 in FIG. 4.

Thermocouples 57 monitor turbine exhaust temperature, which isrepresentative of the turbine inlet temperature. Due to the high levelof turbine inlet temperature, it is not possible to directly measure arepresentative turbine inlet temperature. As seen in FIG. 6B, each modeof power generation has a limiting temperature-P_(2C) curve, and hencerequires a certain fuel flow for a definite average temperature at theturbine inlet.

The two temperature channels are each fed by eight type J(iron-constandan) thermocouples which are paralleled using a swampingnetwork, so that each channel provides an average temperature. Thethermocouples have a range of 550° F.-1150° F. for each channel and areused with analog transmitters of the Bell & Howell 18111A type having anoutput of 4 to 20 ma with reverse action (i.e., 4 ma at 1150° F. and 20ma at 550° F.) and current going to zero upon a channel's thermocouplesfailing open. Both channels are set to give a temperature alarm at 1050°F. The parallel thermocouple paths carry current signals representativeof the two averaged temperatures, and between the paths there isconnected a differential alarm circuit 262, designating a differentialcurrent detector and appropriate alarm circuitry. The alarm circuit 262indicates thermocouple signal differences greater than a fixedpercentage, e.g., 5%, providing a visual or audible signal to theoperator when one path diverges from the other. In this manner, thethermocouple circuits are monitored without causing shutdown. Inaddition, the signals from the thermocouple channels may be directlymonitored (by meters not shown) to provide a continuous indication oftheir condition.

The thermocouple inputs are connected to I/P transducers 212 and 213,which convert the analog input in the range of 4-20 ma to a pneumaticoutput in the range of 3-15 PSI. Thus, the output pressures of thetransducers are proportional to the current input which, in turn, isinversely proportional to the sensed temperature. The outputs oftransducers 212 and 213 are connected to high pressure selector 220,which selects the higher value to prevent shutdown when pressure failureoccurs at the ouput of one of the transducers (the current goes to zeroupon a channel's thermocouples failing open). The output of selector 220(3.15 PSI) is connected to a direct derivative device 228, whichproduces a pneumatic output proportional to the derivative of the input,and which functions to speed up the exhaust temperature control systemto compensate for the fact that the thermocouples react slowly toturbine temperature changes because of their downstream location withaccompanied low gas velocities. The output of direct derivative device228 is connected to the input variable connection of exhaust controller203.

The blade path control path commences with two channels each fed by fourparalleled thermocouples ranged similar to the exhaust temperaturechannel, and indicated at 180 in FIG. 4. The inputs from such channels,at 4 to 20 ma reverse action, representing a temperature differentialbetween 1300° F. and 700° F. respectively, are connected to I/Ptransducers 223 and 224 respectively. Differential alarm circuit 263acts in the same manner as does 262. The transducer outputs, at 3-15PSI, are similarly connected to a high pressure selector 219, whichtransmits the high pressure to input C of controller 204.

The output of transmitter 207 provides a pneumatic signal proportionalto P_(2C) in the range of 3-15 PSI. This signal is transmitted tototalizing relay 190, which also receives a pneumatic signalproportional to ambient temperature T_(IC) (from 71), and produces anoutput proportional to the algebraic sum of such two inputs. The outputof totalizing relay 190 is connected to a first input of solenoid valve179, while the output of solenoid valve 136 is connected to a secondinput of valve 179. The output of valve 179 is connected to the resetinput (designated R) of controller 204. Controller 204 provides directproportional and integral action, the same as exhaust controller 203.Because of the thermocouple locations in the blade path, controller 204gives a better response than the exhaust controller, and accordingly noderivative device is needed to operate on the input. The output of thelow signal selector (LSS) from T231 is used as a feedback signal to boththe exhaust and B/P controllers. This prevents the phenomenon known as"RESET WINDUP".

Comparing FIG. 6A with FIG. 5, the energization of valve 179 (due to thebreaker closing, i.e., 52X) corresponds to gating the P_(2C) signalthrough AND circuit 266. When the breaker is not closed, valve 179 isdeenergized, corresponding to passing a signal through NOT circuit 267and AND circuit 268. In either case, the B/P setpoint signal comes outof the output of valve 179, corresponding to OR circuit 269.

Connected between the LSS output (terminal T231) and the output ofcontroller 203 is a pressure switch 218 which operates a control 218L(FIG. 16) to indicate when the exhaust controller output is the lowsignal, and thus is controlling. Switch 218 operates when its twopressure inputs are equal, or within a fixed limit, and thereby signalswhen the LSS signal is in, fact, the exhaust loop signal. In a similarmanner, pressure switch 238 provides for an indication at 238L (FIG. 16)when the blade path loop is producing the controlling signal.

In operation, when the base load mode is selected, valve 136 isde-energized, such that the signal from transmitter 208, biased withabout 2 PSI at relay 152, is communicated to the setpoint input ofexhaust controller 203, thus providing it with its highest setpoint. Thehighest setpoint for controller 203 yields the lowest output (around 14PSI) upon stabilization of turbine temperature. For peak load operation,valve 136 is energized and valve 137 is deenergized, such that theoutput of valve 136 is biased lower, producing a lower setpoint for theexhaust temperature controller, which lower setpoint in turn makespossible a higher temperature in the combustors by permitting a higherthrottle valve signal for higher fuel admission.

In system reserve load mode, both valves 136 and 137 are energized suchthat there is no biasing of the P_(2C) signal transmitted fromtransmitter 208. In this instance, the setpoint for controller 203 isthe lowest of the three modes of operation, such that the exhaustcontroller output (CO) is accordingly higher for given sensed exhausttemperatures. This permits a still higher controlled temperature in thecombustors via a higher fuel flow. It is to be noted that for exhaustcontroller 203, higher sensed exhaust temperatures produce lower inputsat the input variable C, while the greater the load called for, thelower the setpoint input (since setpoint is inverse to load demand).Consequently a higher sensed exhaust temperature results in a lowercontrol signal, while higher load demand, as set by selection of theload mode, results in a higher control signal.

The blade path temperature control is used as a backup for the exhaustcontrol. For this reason, the biasing of the blade path controller 204is set slightly higher than its normal setting while solenoid valve 179is energized, during which time both the exhaust controller and bladepath controller receive the same changing setpoint derived from theP_(2C) signal. During starting, the blade path control acts as a backupto the speed-load controller, and valve 179 is de-energized such thatthe blade path setpoint is biased higher due to the action of totalizingrelay 190, which biases the P_(2C) signal in accordance with sensedambient temperature. It is to be noted that quick temperature changesare detected and controlled by the blade path control while the exhaustcontrol detects and controls the relatively slow, or steady statechanges.

The means of generating the blade path controller setpoint duringstarting provides the control system with the capacity to vary thetemperature backup control as a function of ambient temperature. A"floating" temperature control line, as illustrated in FIG. 6C, iseffectively achieved to provide changing blade path control between theambient limits of -40° F. and +120° F. The shaded area between the -40°F. and 120° F. lines represents the range of ambient temperaturethroughout which adaptive control is provided. By combining both theT_(IC) and P_(2C) signals in the totalizing relay 190, the setpoint forB/P controller 204 is caused to vary as a function of the ambienttemperature. For a given compressor discharge pressure P_(2C), as theambient temperature goes up (corresponding to normally less availablestarting torque) the setpoint goes up, and as the ambient temperaturegoes down (corresponding to normally higher available starting torque)the setpoint is lowered. Thus, the blade path channel adapts to limitstarting temperatures to a lower than normal level at low ambienttemperatures and to permit higher starting temperatures at higherambient temperatures, thereby compensating for changes in availablestarting torque which result from changes in ambient temperature. Asseen in FIG. 6C, during summer, a higher than normal blade pathtemperature is automatically permitted, while during winter the turbineis constrained to a lower than normal blade path temperature. Theuniqueness of the "summer-winter" control is that, for the first time, aturbine system is provided which not only provides temperature backupcontrol during starting, but which provides an adaptive temperaturecontrol which compensates for performance changes which otherwise occurwith changes in the ambient temperature. While this feature has beenillustrated with a pneumatic embodiment, it is noted that equivalentanalog digital means are also embraced.

In an electrical analog embodiment, the speed changer signal previouslydescribed is provided by a conventional ramp generator. At the breakerclosing, an additional DC signal (of a value according to the desiredstepup in load) is gated with the ramp to provide the stepup in signal.The load changer signal, provided by another ramp generator, is adjustedto provide a ramp which starts from a level equal to the speed signalimmediately after the DC signal has been gated to it. In a similarmanner, the load pickup can be accomplished with a wholly digitalembodiment, the speed control signal having a programmed step up at themoment that the breaker closing is communicated to the control computer.Thus, the technique is equally adaptable to both hardware and softwareembodiments.

Referring now to FIG. 7A, there is shown a block diagram with details ofthe speed and load control paths, and the manner in which the controlsignals derived therefrom are inputted along with the temperaturecontrol signals to the low signal (low pressure) select element 231. Theprimary elements utilized in generating the load and speed controlsignals are motorized regulators, designated load changer 65L and speedchanger 65S respectively. The preferred load changer used in thiselectro-pneumatic embodiment is a synchro-regulator, as manufactured byMoore Products Co., having an AC motor drive and providing a 3-15 PSIoutput. The motor is timed to provide a ramp output from 7 PSI to 16 PSIin 12 minutes. Similarly, the speed changer 65S is suitably a Mooresynchro-regulator providing a 3-15 PSI output, and having an AC motordrive, the motor having a timer set to provide a ramp output from 3 PSIto 15 PSI in 6 minutes. It is understood, of course, that theseoperating characteristics are exemplary only, and may be variedaccording to the application. The electric control of the load changerand speed changer are discussed in more detail hereinbelow in connectionwith the description of FIGS. 11 and 13. As is noted furtherhereinbelow, the functions of 65L and 65S may be performed by electronicfunction generators in an alternate embodiment.

Pressure switch 197, for providing load scheduler wind back, isconnected to the output of load changer 65L. The output is alsoconnected through a first path to amplifying relay 226, and through asecond path to a first input of load scheduler solenoid valve 155. Theoutput of amplifying relay 226 provides the other input to the valve155. When valve 155 is de-energized, corresponding to normal rate ofloading, the unamplified output of load changer 65L is connected throughto one of the six inputs of low signal select element 231. When fastloading is called for, valve 155 is energized, such that the amplifiedoutput from 226, corresponding to 2 minute loading, is connected throughto 231.

The output of speed changer 65S is amplified through amplifying relay232, the output of which is connected to a first input of solenoid valve187. The output of 232 is also connected through bias relay 230, usedfor establishing a higher initial load setpoint, the output of which isconnected to the other input of valve 187. The output of valve 187 iscoupled to the speed load controller 205 as the reference, or setpointsignal.

The inputs to speed transducers 216 and 217 come from separate speedsensors 78, which provide an input in the range of 10-50 ma. Between theinputs there is connected a differential alarm circuit 222 whichprovides an output when the difference between the inputs exceeds agiven amount, e.g., 5%. The outputs of transducers 216, 217 (3-27 PSI)are compared in high pressure select element 218, which selects thehigher pressure and communicates it to amplifying relay 229, and thenceto direct derivative element 227, the output of which is communicated tospeed load controller 205 as the input variable (C). The use of highpressure select element 218 prevents the loss of speed signal andmaximum fuel to the turbine when pressure failure occurs at the outputof one of the transducers. The direct derivative device 227 improves theresponse of the speed control system. Controller 205 is a proportionalaction pneumatic controller, suitably Moore Products Co. model 55A,where the measured variable (C) and the output (CO) are inverselyproportional. The output signal, CO, thus increases with the increasingsetpoint provided from speed changer 65S, and is inversely proportionalto the sensed speed. The output of controller 205 is directly connectedto one of the inputs of the low signal select element 231. A feedback156 from T231 provides the LSS output at point 157. Speed load controlpressure switch 200 is connected between the output of speed loadcontroller 205 and point 157, and activates a panel light 200L (FIG. 16)when the pressure differential thereacross is nomimally zero, indicatingthat the LSS output is the speed output. Similarly, load controlpressure switch 199 is connected between point 157 and the load controlinput to LSS element 231, and activates a load control panel light 199L(FIG. 16) when the pressure thereacross becomes nominally zero. Switches237 and 239 provide similar indications for the load rate path andacceleration path respectively. By this arrangement, the operator has aclear indication of how the turbine is being controlled, and whencontrol is passed from one path to another. The outputs of switches 199,200, 218, 237, 238 and 239 may be connected to a recorder (not shown) toprovide a record of how the turbine has been controlled. It is to benoted that where the signals to the LSS are electrical in form, thecorresponding switches are electronic differential detectors.

Acceleration limit totalizer 209 is employed for surge controlprotection and as a maximum fuel limiter. The output pressure oftotalizer 209 is limited by the surge line pressure and thus limits theopening of the throttle valve. The acceleration limit control isdesigned to control fuel flow before the speed control system comes intooperation at 50% speed. After this portion of the starting operation,the acceleration limit control function only as a backup control. Thesurge maximum fuel line is measured from the compressor dischargepressure which constitutes a first input to totalizer 209. The surgemaximum fuel line is changed when closing the bleed valves such that theacceleration limiter is reset at such moment. This reset is provided bya second input derived from compressor bleed solenoid valve 132, whichprovides a signal when the bleed valves are closed. The totalizer thusprovides an algebraic addition of signals representing compressordischarge pressure and the bleed valve position. This output isconnected to and provides one of the six inputs, designatedacceleration, to low signal select element 231.

The sixth control path which provides an input to LSS 231 is the loadrate limit loop. The LSS output from element 231 is connected to apneumatic load rate limiter 188, which introduces a time delay ofapproximately 2 minutes, such that the output thereof represents thedelayed LPS signal. This output is connected to a bias relay 189, whichfunctions to inhibit the action of limiter 188 during starting andpermit control only during loading. Limiter 188 begins controlling whenits output exceeds the setting of relay 189 at about 25% load. Abovethis point, the output of 189 equals the output of 188 and the timedelay function becomes active.

Making reference to FIG. 7B, the method by which the control system ofthis invention picks up load at the time the circuit breaker is closedconnecting the generator to the load, can be understood. During startup,the speed control channel controls turbine operation. Speed synchro 65Stakes the turbine linearly from about 50% speed up to idle speed wheresynchronization is achieved and the generator breaker is closed. Atbreaker closing, load changer 65L in the load control channel isenergized and produces an increasing ramp output which starts at aminimum load somewhere within the range of 10% to 25%. The load changerproduces a linearly rising signal which increases at a slower rate thanthe speed control signal, such that it takes over control. It is seenthat at the time of breaker closing, the speed control signal isautomatically stepped up through energization of solenoid 187 whichvalves the speed control signal through bias relay 230 so as to add anincrement to the setpoint signal corresponding to the initial step loadrequirement. The amount of this increment can be varied by fixing thebias introduced at relay 230. In this manner, at breaker closing, thespeed control signal is stepped up to the starting level of the loadcontrol signal, which then assumes control due to its lower rate ofincrease. Loading may, of course, then be accomplished in a shorter timethan that programmed by load changer 65L by valving the load changeroutput through amplifying relay 226. There is thus incorporated into thesystem the capability of immediately providing capacity to pick up deadload, such as occurs after power brownouts and blackouts. Thiscapability is combined with continuous temperature backup control fromstarting through load pickup and continuously after steady state load isachieved.

Referring to FIG. 23A, there is shown a modification of the controlsystem of FIG. 7A, wherein the load path is closed loop, providingclosed loop load control. A detector 260 produces an electrical signalrepresentative of load delivered by the turbine-driven generator, andthe load signal is transduced at transducer 261 to provide anappropriate pressure signal. The pressure signal, representing load, isprovided as the input signal to load controller 265, the load controllertaking its setpoint signal from load synchro 65L. The output of the loadcontroller, in this embodiment, constitutes the low signal which isconnected to one of the inputs of the low signal select device 231.

The closed loop load (kilowatt) control functions to maintain a constantload regardless of frequency, compressor efficiency, or ambienttemperature changes. This feature is useful on small systems and inlocations where the day and evening temperatures vary considerably.Normally, as evening approaches the ambient temperature drops and thegas turbine power output increases, or vice versa. This may beundesirable where the load is fixed and, therefore, the operator will berequired to manually compensate for these ambient temperature changes.However, this is not necessary in the closed loop load control system.

The open loop kilowatt control is simpler than closed loop control, dueto providing a fixed fuel input. Load is controlled within a definedtolerance band and the variation is normally acceptable in largersystems. It is also acceptable for "spinning reserve" applications wherethe turbine is being controlled by the loading synchro (65L) at orslightly above minimum load in preparation for an eventual dispatchercall for base load.

It is seen that the turbine load control system, as described above,provides an expanded capability for load control, with the specificcapabilities of varying load setpoint while on speed control or on loadcontrol, with three temperature limiting control curves as a function ofcompressor discharge pressure (i.e., base, peak, system reserve). Eitheropen loop fixed fuel control or closed loop power control with megawattreset capability is available, depending upon the system or userpreference. Means is provided for either normal or fast loading rates.Loading can be accomplished by means of the speed path or load path, byeither open loop load setpoint or closed loop load setpoint. Inaddition, the load can be scheduled as a function of ambienttemperature. Thus, there are provided a plurality of alternativemethods, available to the operator, for obtaining load control. Theseare particularly useful on different types of electrical systems and areemployed for different reasons.

Manual load selection via the speed controller (as discussedhereinbelow) is also available, and is most effective on isolatedsystems where the frequency varies and sudden load increases areprobable. Under these conditions, the speed control responds to pick up25% load (normal) instantaneously, plus additional load, at the ratelimited by the load rate limiter. The load rate limiter functions toprotect the gas turbine from accepting excessive instantaneous load.

D. STARTING CONTROL SUBSYSTEMS 1. Temperature Reset Starting Control

Turbine operation is controlled during a portion of the startup as afunction of both compressor discharge pressure and blade pathtemperature. The turbine is brought up from turning gear speed by adiesel starter to about 20% (Ignition) speed. At this point theadmission of fuel is controlled by the combination of thepressure-temperature (PT) valve 109 and pump discharge control valve 97(FIG. 4). From 20% speed to about 50% speed, the turbine operation isunder control of a fuel (either oil or gas) starting signal derived as afunction of P_(2C) and the B/P signal derived from the blade pathcontroller. There is disclosed, in the next portion of thisspecification, a method of controlling the PT valve to implement a fuelschedule which controls ignition fuel nozzle pressure in a manner so asto improve turbine vane life.

Referring to FIG. 8A, the output of the blade path controller (which isinversely proportional to the detected blade path temperature) isconnected through a bias relay 234 and reduced by a reducing relay 233(reduces the blade path signal to a range of about 0-4 PSI), the outputof the reducing relay being one of the inputs to a high pressureselector 221. The output of the low signal selector is connected topilot relay 235. This relay connects supply pressure (not shown) to itsoutput when the LSS input (which is also the fuel throttle valve signal)reaches the preset value of about 5 PSI. This value corresponds to justabove the point of lifting of the throttle valve from minimum position.The output of relay 235 is connected as a second input to the HPS 221.Thus, until the throttle valve signal rises to about 5 PSI (at about 75%speed) the only input to the HPS is the blade path input. At speedsabove about 75% speed, the blade path signal (reduced at 233) becomesineffective because it is overridden by the LSS signal through the highpressure selector.

The output of high pressure selector 221 (being the B/P signal for about20% speed to about 75% speed) is connected to one chamber of fuelpressure control totalizer 210. Totalizer 210 is supplied with air whenisolation valve 101 is open. Another chamber of 210 receives thecompressor discharge pressure, P_(2C). The totalizer 210 provides anoutput directly proportional to the algebraic sum of the two inputs.Thus, as P_(2C) rises, the totalizer output rises. Also, it is notedthat up to about 75% speed, if blade path temperature rises, the B/Psignal drops, thereby dropping the totalizer output and providingadjustment of the controller reset signal. Above 55% speed, this controlfunction is passed to the LSS signal. The output of totalizer 210 issupplied to a high limit relay 225 which limits the reset signal at 10PSI. This high limit relay functions to limit the maximum oil fuelpressure of the main fuel pump outlet at 950 PSI. The HLR output isconnected to the controller 206 as the reset signal.

The fuel oil pump discharge pressure is converted to a pneumaticpressure by transmitter 236, providing a variable output signal of about3-15 PSI. This signal is connected to the measured variable input (c) ofcontroller 206. Controller 206 is a PI controller (proportional andintegral action) and is reverse acting to produce an output signalproportional to the difference between the variable setpoint signal from225 (introduced at R) and the discharge pressure signal from 236.

The output of HPS 221 is also connected to a gas totalizer 211, whichhas as a second input the P_(2C) signal. Totalizer 211 functions in thesame manner as fuel oil pressure totalizer 210, and produces an outputwhich is limited at 225G. As with the path for developing the oilsignal, it is seen that the signal is limited by blade path temperatureup to about 75% speed, and thereafter is limited by the LSS signal.

The two totalizers 210, 211, the two high limit relays 225, 225G and thecontroller 206 are all supplied with air through isolation valve 101which opens when the machine begins the starting process.

Referring now to FIG. 8B, there is illustrated the manner in which thestarting signals and the throttle valve signal (from LSS 231) coordinatethe controlled starting of the turbine. Fuel oil, from a supply notshown, is connected through the oil throttle valve 99 to the combustionsystem. Similarly, gas fuel may be connected through gas throttle valve99G to the combustion system. When fuel oil is being used, the controlsignal from controller 206 is connected to the pump discharge valve 97,which regulates the pump discharge pressure and which is open atstartup. Valve 97 closes partially in conjunction with the PT limitervalve 109 (FIG. 4) to maintain 200 PSI fuel oil pump discharge pressure.After reaching 20% speed, as the P_(PD) controller signal increases dueto increasing P_(2C), regulating valve 97 is closed as a function ofsuch increasing P_(2C), such that fuel oil pump discharge pressure risesto about 950 PSI at about 50% speed. At 50% speed, the LSS signal risesfrom a minimum of 3 PSI, at which point throttle valve 99 begins toopen, and thereafter the system is controlled through the action of theLSS signal on the throttle valve.

If gas fuel is used, the gas starter signal opens gas starter valve 81,to provide increase of gas fuel to the combustion system between thespeeds of about 20% to 55%. The LSS signal also begins to open the gasthrottle valve 99G at about 50% speed, after which the system is undercontrol of the LSS signal. As shown by the dashed lines, a transferswitch 124 may be employed to transfer operation between fuel oil andgas fuel, or to proportion amounts of respective fuels fed to thecombustion system.

There is thus disclosed a system for temperature reset of the pumpdischarge pressure during starting, which additional temperature controloffers a unique backup capability which improves starting reliability.In the event of a control component failure in the main control loops,or improper throttle valve setting or drift for any other reason, thereexists an additional temperature backup control derived from blade pathtemperature, which maintains control on pump discharge pressure. Becauseof this unique reset capability, the number of transient temperatureexcursions above the absolute turbine trip level are minimized andthermal shock is avoided. After the turbine has attained a speed ofapproximately 75%, this temperature control loop is effectivelydeactivated due to the action of relay 235, and temperature control ispassed to the low signal select signal.

2. Ignition Pressure Control Subsystem

As has been set forth hereinabove, the turbine system of this inventionis provided with a bypass pump pressure regulator valve 97 and a bypasslimiter valve 109, which valves function together to provide stable fuelpressure operation during ignition and other turbine operating periods.

With respect to plant startup operations, a plant which has fast startupcapability and high reliability is characterized as having highavailability, which is a factor especially important to peakingapplications of gas turbine electric power plants. Reliability in largemeasure results from the plant design and the quality of plantmanufacture, and is enhanced by the basic design of the control. As seenabove, the control design of this invention includes multiple provisionsfor controlling or limiting particular plant variables. Thus, plantavailability is enhanced through reliability by multiplicity.

Normally, faster gas turbine plant startups cause greater temperature orthermal stress cycling damage to the turbine blades and other metalparts. Therefore, some balance must be achieved between startup speedand turbine life, i.e., the long term cost of turbine damage caused bythermal stress cycling. To improve the plant life expectation or toimprove startup availability of gas turbine electric power plants byfaster startup without added metal damage, it is desirable to identifyavoidable causes of stress damage and determine improvement means bywhich such damage can be avoided compatibly with all other plantoperating considerations. Added benefit is realized if the improvementmeans also provides reliability by multiplicity.

One cause of thermal stress damage occurs in the supply of fuel, andespecially liquid fuel, to the turbine nozzles. In the turbine plant ofthis invention, liquid fuel is supplied to the turbine from a fuelsource by a turbine driven pump. The pump develops fuel pressure as afunction of the turbine speed, and the nozzle fuel pressure is typicallykept within tolerances by positive regulation of the pump dischargepressure. Fuel pressure regulation is achieved by regulating the flow ofbypass fuel from the fuel supply line back to the fuel source. Fuelpressure fluctuations due to transient conditions not correctable by thepressure regulator can cause excessive thermal stress cycling of theturbine metal parts during ignition and at other operating time periods,including idle operation and light load operation.

The PT limiter valve 109, which is in parallel with the bypass 97, isutilized to optimize the responsiveness of the bypass subsystem duringignition and other operating time periods, to prevent rapid transientfuel pressure oscillations and thermal cracking of turbine vane sectionsattributable to differential expansion of components. A suitable PTlimiter valve is disclosed in detail in co-pending U.S. application Ser.No. 261,192, filed June 9, 1972, and assigned to this assignee. Thesubsystem disclosed herein provides an improved method and apparatus foraiding combustor light-off by optimally scheduling the combustor nozzlepressure.

Referring to FIGS. 8C, 8D and 8E, there are shown means for controllingthe PT limiter valve, and the consequent method of controlling nozzlepressure, to provide an optimum sequence of nozzle pressure duringignition and startup. Before the isolation valve 101 is opened andignition is commenced, the nozzle pressure is at 0 (throttle valve hasnot been raised) and the PT limiter valve 109 is at a low prefireposition. When ignition is commenced, light-off of the combustors isaided by raising the nozzle pressure to a high value, e.g., 10 PSI. Thisnozzle pressure is referred to as the "pop" pressure, and is maintaineduntil flame is sensed. The time during which nozzle pressure is raisedto and maintained at the "pop" pressure is referred to as the popperiod.

Upon detection of flame, the PT valve 109 is dropped to a lowerposition, producing a drop in nozzle pressure during a timed periodwhich is referred to as the "glide" period. During the glide period, thenozzle pressure ramps upward, due to the action of the reset subsystem,as described immediately hereinabove. At the end of the timed glideperiod, the PT valve returns to its full position (run position),enabling buildup of nozzle pressure under speed control. The glideperiod provides the turbine with a period of reduced fuel inputimmediately after detection of flame, so that the thermal impact uponthe turbine is lessened, thus reducing thermal strain.

The pop and glide fuel schedule is accomplished by a unique method ofcontrolling the PT limiter valve. When fuel is on, corresponding toopening of the isolation valve 101, switch 271 provides power through tothe sequence circuitry, as shown in FIG. 8C. This immediately commencesoperation of ignition timer 273, which times the length of ignition. Atthe same time, isolation valve 101 provides air pressure throughde-energized pop and glide valve 277, thereby providing an input topositioner 109P which causes setting of the PT valve 109 to its full, orpop position. When the nozzle pressure reaches its predermined (pop)maximum, nozzle pressure switches 275, 276 cause closing of theirrespective contacts, thus initiating pop timer 274, which times outthrough self-operated contacts 274-1, which times out throughself-operated contacts 274-1. Nozzle pressure is limited at the poplevel by positioner 109P. When light-off occurs as sensed by the flamedetectors, the popping pressure is reduced to the glide requirement.Therefore, the pre-set time period determined by the pop timer is themaximum time that the popping pressure can exist, since the pressure isautomatically reduced when and if flame is established. It is to benoted that, since the pop timer is initiated by the pressure switches275, 276, the time period during which pop pressure is maintained islimited, thus limiting the initial thermal surge.

When flame is detected, contacts FLM7 and FLM8 close, initiating glidetimer 272, which times out a glide period in the range of 70 to 140seconds. Relay FLMX is energized and maintained closed through contactsFLM1. Contacts FLM2 are also closed, thus energizing solenoid 279, whichenergizes pop and glide valve 277. This provides a decreased pressuretransmitted through pop and glide regulator 278 to positioner 109P,resulting in changing to the lower PT valve position. As describedbefore, this provides a corresponding drop in nozzle pressure. At theend of the timed glide period, contacts 272S are opened, thusde-energizing solenoid 279, and the PT valve returns to its full, or runposition. Note that the pop and glide solenoid must be energized toglide, and consequently permits full load operation in the event ofsolenoid failure. Failure of the solenoid during starting results ineither over temperature control or over temperature shutdown on bladepath position. If failure results in continued pop pressure over theestablished pop time period (maximum of 15 seconds), a second time checkset at 2 additional seconds actuates an alarm to indicate that the popand glide is non-operative. Failure to light off with the pop systemwithin the allowed ignition period results in dumping of the overspeedpressure purging in a second repeated pop and glide attempt.

While the preferred embodiment of the "pop and glide" apparatus iselectro-pneumatic, it is understood that other forms are readily adaptedto the turbine power plant. For example, where a digital computer isutilized, ignition start, pressure switch and flame detect signals areinputted to the computer, and PT valve position signals are outputted,with the sequencing and logic functions being provided by the computer.

Referring now to FIGS. 9 and 10, there are shown curves representing atypical start and a typical loading, respectively. These curvesillustrate the operation of the control system as has been described tothis point. Referring first to FIG. 9, there are plotted curves of LSSinputs against time, for a typical start. Those inputs which are lowest,and therefore controlling, are shown as solid curves, while thenon-controlling inputs are represented by dashed line curves. From thetime of startup, until the time designated as A, the turbine is broughtup to speed under the action of the diesal starter. At time A, andextending to time B, the turbine is under control of the PT valve. Attime B, control is switches to the fuel pump discharge pressure control,as illustrated in FIGS. 8A and 8B. At time C, the turbine is placedunder speed control, and thereafter is under throttle valve control, thethrottle valve being controlled by the LSS output signal.

In FIG. 9, the solid line represents the minimum input to the LSS, andthus the LSS output. The dashed lines represent other LSS inputs. theload scheduler and load rate limiter signals are shown as constantsthroughout the typical start procedure. The acceleration signal is seento be the low input, and thus the LSS output, up to the point wherecontrol is passed to speed control, corresponding to about 50% speed.However, during this time the acceleration signal does not control theturbine since its value is less than 3 PSI. It is to be remembered thatthe throttle valve does not commence lifting until the LSS signalexceeds 3 PSI. From 50% speed on, the speed control signal, generatedfrom the unit 65S, is the controlling signal. It is noted that atrelatively low speeds, the blade path input signal is quite high, but isreduced in magnitude to a minimum value roughly corresponding to thepoint where the speed changer starts to produce the ramp output forspeed control. For higher speeds, the blade path signal again increases.This reflects the fact that at lower and higher speeds, the blade pathtemperature is generally lower, and that the blade path temperaturegenerally maximizes at or near 50% speed. Of course, it is to beunderstood that if, for any reason, the blade path temperature were tobecome sufficiently great such that the blade path curve were to dipbelow the speed control curve, then the B/P signal would take overcontrol of turbine operation, thus limiting speeds.

Referring now to FIG. 10, there are shown typical loading curvesrepresenting LSS inputs as a function of time, during a normal loadingprocedure. Also indicated is the load, in MW, corresponding to thelimiting load control signal. The heavy continuous line represents thelowest of the inputs to the LSS unit, and consequently the LSS outputwhich controls the throttle valve. Time is designated as starting at thepoint when the breaker is closed, the turbine being at synchronous speedand being presumed to be maintained at synchronous speed throughoutloading. At time of breaker close, there is an immediate stepup in power(to approximately 3.5 MW), as accomplished by the load pickup meansdiscussed elsewhere in this specification. At that time, the load signalgenerated by unit 65L starts to ramp upward, and for a period of time isthe controlling signal. The load rate limiter output takes control afterbreaker close, and controls the loading operation until the exhausttemperature control signal drops to a lower level, at which time theturbine is in temperature control.

As explained elsewhere in the specification, immediately after thestepup of the speed control signal, to provide the initial stepup inload, the speed changer 65S ramps upward at a high rate, and, except formanual operation described hereinafter, is not a control signal duringloading. The load output from unit 65L ramps at a constant rate to 15PSI. The load rate limiter signal is time delayed with respect to the65L output, and rises at a slower rater of increase, such that it takesover control from the load signal shortly after breaker close(approximately two minutes after breaker close). The accelerationlimiter output does not participate in control of loading. It is shownas rising, due to the fact that its output goes up as P_(2C) goes up.The exhaust temperature and blade path temperature control curves areseen to drop down at a substantially constant rate with increasedloading of the turbine, reflecting the fact that as the temperature goesup from turbine loading, the temperature control signals go down. Theblade path control signal, during most of the starting period, is thelower signal, due to its quicker temperature response. During loadingboth the exhaust temperature controller and blade path temperaturecontroller receive the same reset signal, since solenoid valve 179 isenergized. However, during steady state operation the blade pathtemperature control is used as a backup for exhaust control, andtherefore the biasing of blade path controller 204 is put slightlyhigher while valve 179 is energized, such that the blade path controlleroutput is slightly higher. This is seen from the curves, it being notedthat each controller reaches its setpoint corresponding to an output ofapproximately 14 PSI, with the exhaust controller output being slightlylower, and accordingly being the controlling output.

E. SPEED AND LOAD CONTROL CIRCUITS

Referring now to FIG. 11, there is shown a schematic diagram of aportion of the speed mode control circuits used in the control system.The circuit diagram of FIG. 11, like that of the other circuit diagramfigures, has bus bars marked (+) and (-) respectively. Unless otherwiseindicated, the voltage across such bars is 110 volts DC. It is, ofcourse, understood that other voltage values may be utilized accordingto particular designs. Respective parallel paths between the two busbars are numbered, and reference will be made throughout the followingdiscussion to different circuits by their respective circuit numbers.

A "lower" push button 148L and "raise" push button 148R are connected inseries with relay coils LX and RX respectively, at circuits 170 and 171.Energization of LX permits lowering of speed or, in certain modes, load,and energization of relay RX permits raising of speed or load. Thechoice of controlling either speed or load is made at other points inthe control circuitry. The circuits for lowering the output of speedchanger 65S are shown at circuit 172, while the circuits for raising theoutput of speed changer 65S are shown at circuit 173. When the generatorbreaker is open, relay 52X (circuit 178) is unenergized and contacts 52Xremain closed. If control is local (see FIG. 24, circuits 242, 243)relay LX is energized, and contacts 52X are closed, speed changer lowerrelay 65SL may be energized by operator push button through the actionof the closed LX contacts, upon the condition that relay 65SR is notenergized. When master switch 4Y1 contacts are closed (circuit 244) andthe speed changer wind back relay 195X (6319SX) is energized (circuit179), relay 65SL is energized and the speed changer output is lowered.Likewise, for manual control, the synchro switch SSX in the synchocircuitry is closed, and the breaker is open so that contacts 52X areclosed. When switch 148L is closed and the ready to load contacts RTLXare closed (this occurs when certain permissive conditions are met),65SL is energized through the closed wind back contacts 195X. Finally,65SL is also energized when synchro switch SSX is closed and the autosynchronizing relay (not shown) is energized, closing contacts 255.

Speed changer 65S is raised by energization of relay 65SR, under similarconditions. Energization of relay RX causes energization of relay 65SRthrough closed contacts RX when in local operation and before thegenerator breaker is closed. Closing of synchro switch SSX and fieldbreaker contacts 255 also causes energization. When raise button 148R isclosed, 65SR is energized (circuit 173) through the synchronizingcircuit as long as the normal stop contacts NS1 are not opened, thespeed changer has not reached its maximum output (194 remains closed),and the ready to load contacts RTLX are closed. 65SR can also beenergized through normally closed contacts TSLX (closed as long as theturbine is not in the base, peak or system reverse load mode) uponclosing of the generator breaker contacts 52X, or when the 50% speedswitch contacts 201 are closed and the turbine is not ready to load(RTLX contacts closed). Closing of contacts 201 at 50% speed providesnormal automatic energization of speed chamber 65S, to produce an upwardramp, during the normal starting procedure, and before ready to load.

Referring to circuit 174 there is a schematic diagram of the componentsof speed changer 65S. It is seen that an inverter 65SI provides ACpower, which is connected across the RAISE coil when contacts 65SR areclosed, and across the LOWER coil when contacts 65SL are closed,corresponding to energization of relays 65SL and 65SR respectively.

Referring now to FIG. 12, there are illustrated circuit diagrams of theload control circuits. The auto load scheduler 65L is shown at circuit135 and, like the speed scheduler 65S, has an inverter 65LI and RAISEand LOWER operating coils, energized through contacts 65LR and 65LL,respectively. At circuit 133, it is seen that relay 65LL is energized,thereby closing contacts 65LL and causing the output of the auto loadscheduler to be lowered. When the load scheduler wind back pressureswitch 197 (circuit 177) causes closing of contacts 197X (6319LX), the37LX contacts are closed (they open above 10% load; see circuit 139),and either minimum load has been called for (thus closing contacts MX2)or a normal stop has been called for, thus closing contacts NS1 (circuit145). Referring to circuit 134, it is seen that 65LR is energized underthe conditions where the generator breaker has been closed, thus closingcontacts 52X, normal stop is not called for, the load scheduler has notreached its maximum position (such that contacts 196 (6318L) remainclosed), and the turbine is in either base, peak, or system reverseoperation. At circuit 140, solenoid 187 (20-20) is energized at breakerclosing to give the initial load setpoint, as discussed with respect toFIG. 7B.

The fast loading controls are illustrated at circuits 141 and 143. Afast loading push button LF is provided at both a local (L) and remote(R) location, and when depressed causes energization of coil FLX, uponthe condition that contacts RTLX are closed. Upon energization of coilFLX, contacts FLX are closed, thus holding coil FLX energized afterbutton LF is released, under the condition that master switch 4Y1 isenergized (thus closing contacts 4Y1). As long as coil FLX is energized,load scheduler solenoid valve 155 (20-19) is energized (see FIG. 7A),thus causing an increase in the rate of increase of the output of loadchanger 65L.

Circuit 145 shows the normal stop control circuitry. A push button NS isprovided at both local and remote locations, and when depressed causesenergization of coils NS1 and NS2. These coils are self-locking throughcontacts NS2 as long as master relay 4Y is energized, closing contacts4Y. Coils NS1 and NS2 can be de-energized, thus holding the normal stopcontrol, by pressing the NSC cancel button at either the local or remotelocation.

Referring now to FIG. 13, there are illustrated circuit diagrams of theloading mode control circuits used in the control system of thisinvention. The circuits are designated as those which control theminimum load mode, base load mode, peak load mode and system reversemode, respectively. Corresponding to each mode, circuits are designatedwhich control operating and reset functions.

The operating circuit for the minimum load control is at 110, and thereset circuit at 111. Minimum load control is obtained by temporarilyclosing the LM contacts, in either local or remote control. Closing theLM contacts causes energization of the operation (O) coil of relayM_(x), and switching of the M_(x) switch to the reset (R) circuit. Thiscauses closing of the M_(x) contacts at circuit 112, and energization ofrelays MX1 and MX2. Upon energization of relay MX2, contacts 4XA(circuit 245) are opened, such that the reset portion of M_(x) is notenergized after the LM button is released and the LM contacts in circuit111 have been closed. However, upon de-energization of relay 4XA, oroperator placement of control into either the base mode load, peak loadmode or system reverse mode, contacts BX1, PX1 or SRX1 are closed,causing reset of the M_(x) switch to contact the operating M_(x) coil,whereupon the M_(x) contacts are opened and control is taken out of theminimum load mode.

The base load and peak load control circuitry is identical inconfiguration and operation to that of the minimum load circuitry.

The system reverse circuitry, circuits 126-129, is identical to theminimum load circuitry, with the exception of contacts 52X in circuit126, providing that the generator breaker need be closed before theturbine can be put in system reverse control. In addition, at circuit122a, coil 131 is energized when the system is either in peak load orsystem reserve control, thereby energizing solenoid valve 136 (FIG. 6A).Also, at circuit 129, when the turbine is placed in the system reservemode, contacts SR_(X) are closed, thus energizing solenoid valve 137(also discussed in FIG. 6A).

Referring now to FIG. 24, the master relays are shown at circuits 244and 245. The trip reset contacts 259 comprise a series of contactswhich, when closed, energize relay 4Y. These contacts are set forthhereinbelow in Table B. The RTS contacts are closed when all thepermissives set forth in Table B are met. Upon closing of the trip resetcontacts and the RTS contacts, and placement of the turbine system inminimum, base or peak mode, master relay 4XA is energized, which is selflocking through contacts 4XA. Closure of contants 4XA, along withclosure of contacts 257 (the lube oil pressure switch) energizes timerTD2 which times out 20 seconds, and then through closure of contacts TD2energizes master relays 4, 4Y1 and 4Y2.

Referring to circuits 337, 342-344 (FIG. 24) and 251, 355-58, 360-64(FIG. 25), there is illustrated the circuitry for controlling theignition sequence. When the turbine reaches ignition speed, pressureswitch 70 closes, energizing coils 70X1 and 70X2. Closure of contacts70X2 energizes solenoid 178, the purge relay PGX having been initiallyenergized (circuit 364) to close contacts PG. Energization of solenoid178 causes a buildup of overspeed trip air pressure, closing contacts147, which remain closed as long as the air pressure is maintained abovea predetermined limit. This causes energization of relays 198X1 and198X2, in turn energizing relay 198X. Energization of relay 198X1 allowsignition (circuit 355) by energizing solenoid valve 119 (see FIG. 4).Additionally, energization of 198X1 energizes the ignition transformer250 (circuit 251). As seen at circuit 356, energization of 198Xinitiates timer TD1, which times out 35 seconds for establishing flameon both detectors. After 35 seconds, timer TD1 pulls in. If flame isestablished in all combustor baskets, contacts 7A2 or 7B2 and 8A2 or 8B2of the flame detection monitors are actuated, whereupon flame detectionrelay FDX is energized. After the 35 seconds timed out by TD1, relayTD1X2 is energized (circuit 363), energizing relay TD1Y (circuit 357),which causes de-energization of the ignition transformer. The purgerelay PGX (circuit 364) remains energized, and the flame detect light islit (circuit 360).

However, if both flame detectors of basket 7 or 8 sense loss of flameafter the 35 second ignition period, neither relay FDX nor TD1Y areenergized, and the purge relay PGX is de-energized. This causesde-energization of the overspeed solenoid 178, and consequently theoverspeed pressure disappears. As a result, contacts 147 open and relays198X1 and 198X2 are de-energized, the ignition transformer beingswitched off as a consequence. As seen at circuit 361, de-energizationof 198X2 also closes the circuit to counter 79, causing it to countdown. Counter 79 may be reset from 2 shot line 618, and thus a secondstartup is permitted automatically. Similar logic circuitry, not shown,provides for shutdown in case of "outfire" or loss of flame, duringrunning. If flame is lost at both sensors of either basket, immediateshutdown is effected and an alarm is set. At the same time, thedetection of flame loss at any one of the four detectors is signaled bya respective outfire lamp, to indicate the condition to the operator. Ifonly one sensor of either basket indicates outfire (in which case thesensor or related circuitry is at fault), system operation ismaintained.

F. TWO SHOT SHUTDOWN

A two-shot shutdown control is provided in the system of this inventionwhereby an automatic procedure permits multiple restarting remotely,under selective malfunction, without jeopardizing turbine life. When aturbine malfunction occurs causing shutdown, the control system isautomatically reset when the condition is corrected after the firstshutdown. If a second shutdown signal occurs within a preset time(adjustable) of the first shutdown while the unit is starting orrunning, the control is locked out of automatic restart. The system canthen only be started by manual control (at the turbine, not at theremote control) by the local maintenance operator. However, if a secondshutdown does not occur within an hour, the control is automaticallyreset to a two-shot condition, such that restart is again availablefollowing the next shutdown.

In accordance with the above, the control system providesdifferentiation and proper response for the following three conditions:

1. Alarm only--Multiple restarts unlimited.

2. 1 shot shutdown--Malfunction implies possible damage if restarting ispermitted.

3. 2 shot shutdowm or multiple--Permits multiple limited restartingattempts after abort and within a prescribed time period.

Referring to FIG. 14B, there is shown an OR gate having a plurality ofinputs, each connected so as to transmit a signal representing thefailure of a condition requiring shutdown. Examples of such conditionsare de-energization of the exhaust temperature relay, blade path relay,and vibration relay (due to fail-open of a respective switch). Theoutput of the OR gate is connected to an AND gate, having a second inputfrom master output (4Y1). Thus, whenever the master control relay isenergized and any one of the two-shot shutdown conditions exist, anoutput is passed to the shutdown counter. The counter is normally set at2, and counts down in increments to 1 and 0. The counter has two outputterminals, for transmitting signals when the counter has counted down to1 and 0 respectively, and an automatic reset terminal for introducing asignal to reset the counter from 1 to 2.

In operation, upon the first shutdown, the counter counts down to 1,causing a trigger signal to be connected to the one hour timer (TD8). Atthe end of one hour, an output signal is generated by the timer which iscoupled to the reset terminal of the counter. If the counter is still at1, it is reset to 2. If it is at 0, it cannot be reset by this signal.As shown, the counter may also be reset to 2 through a manual resetcircuit located locally at the turbine. If two shutdowns occur within anhour, a lockout signal appears at the 0 count terminal, and the countercannot be automatically reset.

Referring now to FIG. 14C, there are shown the conditions which must bemet for automatic restart. Three inputs are connected to an OR circuit,carrying signals designating that the system is in either the minimum,base, or peak load state. When the system is in any one of suchconditions, the OR circuit produces an output signal, designated the LSX(load select) signal. When this signal is present, and the lockoutsignal is not present, the two-shot restart signal R2X is generated,which permits automatic restart when the shutdown condition iscorrected.

As seen in FIG. 14A, there is shown at 164 a manual push button 241 inseries with reset relay RRX. The counter (designated 79) is shown atcircuit 166, in series with switch 4Y1 (closed when the master relay isenergized), and in series with a plurality of switches connected inparallel. These switches constitute the OR circuit, as shown in theupper block diagram, and are normally open when conditions aresatisfactory. When a malfunction occurs for which a second try ispermitted, the corresponding switch in circuit 166 is closed, thustriggering counter 79. The reset terminal of counter 79 is connectedthrough switch TD8-1 to the positive bus line, and through diode 76.1 tothe manual reset line 619.

At circuit 167, the timer TD8 is shown in series with normally openswitch 79-1 (which closes when the counter counts to 1) and normallyclosed switch 79-0 (which opens when the counter counts to zero). Alsoin series with switch 79-0 is switch LSX and relay R2X. At circuit 181,parallel switches MX1, BX, and PX form the OR circuit shown in the lowerblock diagram, and are in series with relay LSX. Switch R2X, closed whenrelay R2X is energized, is connected between the plus line and line 618(two-shot line). Switch RRX, closed when reset relay RRX is energized,connects the plus line with both line 618 and the one shot bus resetline 619.

Circuit 183, the blade path temperature start circuit, contains bladepath switches 295.1 and 295.2 in parallel, which switches are normallyclosed when the temperature is below 1300° F. These switches are inseries with relay BSX. It is seen that when only one of the twothermocouple switches fails open, the circuit is not affected. However,when both fail open (both sense temperatures exceeding 1300° F.) relayBSX is de-energized. This in turn causes the opening of a switch (notshown) in the shutdown circuit, causing system shutdown. The twotemperature switches are connected through seal contact BSX to the plusline, and through blocking diode 76.13 to one-shot line 619.

In a similar fashion, shutdown relays BRX (circuit 184) and EX (circuit185) are de-energized upon fail open of both of a pair of thermocoupleswitches. These circuits are connected through diode 76.14 and 76.15respectively to two-shot line 618. At circuits 190 and 192, thevibrations and bearing temperature circuits respectively, the normallyenergized relays VBX and BT1X respectively are de-energized upon failopen of any one of the series contacts. The vibration circuit isconnected through diode 76.20 to the two-shot line 618, and the bearingtemperature circuit is connected through diode 76.21 to the one-shotreset line 619.

The operation of the two-shot control can be illustrated by examinationof malfunctions of one of the turbine functions. For purposes ofexamination, it is assumed that the malfunctions occurs in the turbineexhaust temperature limit circuit 185. When both switches 295.5 and295.6 open, representing detection of exhaust temperature greater than1050° F., relay EX is de-energized and contact EX at circuit 166 isclosed, setting counter 79 from 2 to 1. At the same time, another EXcontact in the shutdown circuit (not shown) is open, causing shutdown ofthe turbine system. Under these circumstances, switch 79-1 in circuit167 closes, initiating timing of a one hour period at timer TD8.Assuming selection of either manual, base, or peak operation at circuit181, contact LSX is closed, causing energization of relay R2X andclosing of switch R2X, such that the positive line is connected throughto the two-shot line. Under these circumstances, it is seen that as soonas either one or both of the switches 295.5, 295.6 closes again,representing correction of the shutdown condition, relay EX isre-energized through diode 76.15. The shutdown circuit is then reset,permitting system restart. Assuming no further shutdowns, timer TD8times out one hour, at which time switch TD8-1 closes, transmitting areset signal to counter 79, resetting it to a 2 count.

If, after automatic restart, a second shutdown occurs before the onehour period terminates, counter 79 is counted to 0. Switch 79-0 atcircit 167 then opens, causing de-energization of relay R2X and openingof contact R2X, such that two-shot line 618 is not energized. Underthese circumstances, the shutdown relay (e.g., EX) cannot be energizedfrom the two-shot line even when the condition is corrected (or correctsitself). When the one hour is up, the signal through switch TD8-1 doesnot reset the timer, as this reset signal cannot reset it from a countof 0. The system can be restarted, and the counter reset only by thelocal operator by depressing push button 241. This causes closing ofrelay contact RRX (circuit 183) which connects positive voltage to thetwo-shot line 618.

The operation of the automatic turbine control restart circuitry isillustrated in FIG. 14D. At time T₁, the malfunction occurs, causing afirst abort. At time T₂, the malfunction is corrected or correctsitself, and turbine restart is automatically enabled. At time T₃, at thespeed where the malfunction occurred during the first start, themalfunction does not re-occur, permitting continuation of a successfulpart. This action provides safe automatic turbine control restart,without a second command during the time the unit is decelerating. Thisoption enhances the turbine starting reliability by permitting thestarting control to automatically re-sequence for those type ofmalfunctions that may not occur on the second try. It is to be notedthat more than two "shots" may be programmed for different malfunctions,the number of shots allocated to each condition being a matter of designchoice.

Referring now to FIGS. 15-21, there are shown block diagrams of thespeed and load control functions performed by the apparatus of thisinvention. The functions described are carried out by the apparatus ashereinabove described. However, it is to be understood that where suchfunctions have been described as being carried out by pneumatichardware, they can also be carried out by equivalent solid statehardware. For example, the speed changer and load changer functions maybe performed by equivalent electronic function generators. In a similarmanner the pneumatic controllers, totalizers, limiters, etc. may bereplaced with equivalent solid state devices.

Referring now to FIG. 15, there are shown the conditions for achievingminimum load control. When the breaker has been closed and 99% speedattained, the output of the speed changer is adjusted upward accordingto the initial load setpoint. This upward adjustment brings the speedchanger output directly up to the load scheduler minimum output (seeFIG. 10. Under the conditions where the load scheduler is not energized,the speed load controller output produces the minimum signal which iscommunicated to the throttle valve, causing the load to increase tominimum load. As soon as the load scheduler begins to produce a rampoutput, it takes over control and the turbine passes from minimum loadcontrol.

Referring now to FIG. 16, there is shown a block diagram of the baseload control apparatus of this invention. The turbine, when ascending tobase load, may be under control of the speed load controller, the loadscheduler, the blade path controller, or the temperature exhaustcontroller, depending upon which of these is producing the lowest outputsignal. Note that, for any given day, base load is only a load pointcontrolled by temperature control. The ramp generators are used toascend to "base" and descend from "base", but it is the temperaturecontol which maintains the turbine at base load. See FIG. 10, whereafter the 12 minute ramp, the exhaust temperature signal is controlling.When the generator breaker has been closed but the speed changer limithas not been reached, the speed changer produces an output which, whenmodified by the initial setpoint step up, forms an input to the speedload controller which provides an output during the time period from theclosing of the generator breaker to initial load scheduler action. Aload scheduler output is produced when the base load mode has beenselected and as long as the load schedular limit has not been reached.If the fast load mode has not been selected, the load scheduler outputproduces an output for normal loading, nominally in 12 minutes. If theoperator has made a request for fast loading, the load scheduler outputis modified to produce a fast loading signal, causing loading of theturbine in approximately 2 minutes.

Still under base load control, when the generator breaker has beenclosed and base load has been selected, the P_(2C) signal is combinedwith the blade path temperature signal to produce an input to thetemperature controller, which provides a transient backup signal which,if lower than either the speed load controller or load schedulersignals, provides control of the throttle valve through an OR gate (thelow signal select device 231). Similarly, when base load has beenselected, the P_(2C) signal is combined with the temperature exhaustsignal and forms the input to the temperature exhaust controller,producing a steady state backup signal, as a second temperature backupthrottle valve control. Thus, under base load control, after thegenerator breaker has been closed the speed load controller signalcontrols the throttle valve for the short period of time until the loadscheduler signal assumes control and ramps the turbine up to base load.During the increase of load, both the blade path and exhaust signals areavailable as backup control signals. When the exhaust temperature signalbecomes the smallest signal, it maintains the turbine at base load (seeFIG. 10).

Referring now to FIG. 17, there is illustrated a block diagram of themeans for providing control in the peak load mode. As with the base loadmode, the load control signal which controls the throttle valveoperation during ascent to "peak" may be derived either from the speedload controller or from the load scheduler. Again, when the generatorbreaker has been closed and the speed changer limit has not beenreached, the speed changer provides an output which, adjusted by theinitial load setpoint, provides an input to the speed load controller.It is to be noted that as soon as the speed changer limit is reachedswitch 194 opens to stop the synchro ramp. The load scheduler continuesto produce an output as long as the load scheduler limit has not beenreached (switch 196 not open). However, as with the base mode, when theexhaust temperature setpoint is reached, the exhaust control takes over.The choice of load control determines the setpoint, and accordingly thesteady state load level.

Referring to the blade path loop, it is seen that a signal representingP_(2C) is produced when the generator breaker is closed, and is afunction of whether the turbine system has been placed in peak loadand/or system reserve load mode. This relates to the energization orde-energization of solenoids 136 and 137 respectively, which alter thebiasing of the P_(2C) signal which acts as a setpoint signal to theblade path controller. Similarly, the choice of load mode controlaffects the P_(2C) signal which combines with the temperature exhaustsignal to provide the inputs to the temperature exhaust control.

FIG. 18 illustrates the control when in the system reserve mode. Thiscontrol is similar to that as described hereinabove for peak modecontrol, with the choice of system reserve mode altering the setpointP_(2C) signal for the blade path controller and exhaust temperaturecontroller respectively.

Referring now to FIG. 19, there is shown the block diagram for fastloading selection. Fast loading may be selected either remotely (R) orlocally (L). When such selection is combined with closing of the masterrelay, and the turbine has not passed 99% of full speed, a request forfast loading signal (FLX) is produced. If a flame is also detected, anoutput is provided to the fast loading pulse counter.

FIG. 20 represents the functional conditions for speed control duringstartup, or starting fuel control. The detection of instrument air,blowdown valve close, the P_(2C) signal and to the ambient airtemperature signal, as well as the absence of any load control, producesa signal (representative of P_(2C)) which is combined with a blade pathtemperature signal to provide the variable and setpoint inputs for theblade path controller. The output of the blade path controller can beutilized as a signal in controlling the starting valve for speeds up toabout 45%. For speeds from about 45% to 100% of synchronous speed, speedcontrol is normally effective as the main control parameter via speedload controller. For speeds less than 95% when the bleed valves areopen, the acceleration limiter produces an output which is a linearfunction of P_(2C). For speeds greater than 95%, when the bleed valvesare closed, the acceleration limiter is translated downward butcontinues as a linear function of P_(2C). The lowest selected signalamong the acceleration limiter, the blade path signal, and the speedload controller signal, is delivered to the throttle valve. For speedsgreater than 2100 r.p.m. (45%) and less than 99%, with the turbine notready to load (RTL), there is produced a linear ramp speed changeroutput. If the system is ready to load and speed has passed over 99%,and the system is in automatic or manual synchro, the speed changer alsoprovides an output. The speed changer output and the speed signal arecombined to produce an error signal at the speed load controller whichprovides speed control from 2100 r.p.m. to synchronous speed.

Referring now to FIG. 21, there is shown a block diagram for thefunctional operations under manual load control. When the operator hasplaced the system in base, peak, or system reserve control (but notminimum load), and the load scheduler limit switch has been closed(indicating that the load scheduler went to maximum position) manualload control through manual operation of the speed changer may beachieved. The operator may choose to raise or lower load and may do soby manually depressing either a RAISE or LOWER manual control button,under the conditions where the load is above minimum load, and as longas the speed changer limit switch is not closed (the speed changer hasnot reached its maximum position). Under these conditions, manualpressing of either the RAISE or LOWER button causes correspondingincreasing or decreasing output of the speed changer 65S, producing anoutput from the speed load controller which is lower than the output ofthe load scheduler, thus providing control of the throttle valve betweenloads of 10% and 100%. In the increase loading direction the load ratelimiter imposes a time delay in the manual load mode. It is inactive inthe lower direction.

G. SPEED-LOAD HOLD AND LOCK SUBSYSTEM

Referring now to FIGS. 22A and 22B, there is shown an alternateembodiment of the speed and load control circuits, which alternateembodiment is designed to give the operator greater flexibility andchoice for holding and locking any desired load level. This embodimentprovides a degree of operator flexibility not previously available inany other known analog or digital control system for a turbine. In thefollowing discussion of FIGS. 22A and 22B, reference will be made to theindividual circuits which comprise the subsystem, which are designed bycapital letters.

Most of the circuit components of the subsystem of this embodiment aresimilar to those described hereinabove, and in such cases the samenumeral identifications are utilized. The primary component differencein this embodiment is that the loading synchro is comprised of twodistinct loading synchros, namely a 12 minute loading synchro designated65L-2, which provides a linear ramp loading signal which reaches itsfull output in 12 minutes, and a two minute loading synchro 65L-1 whichreaches its full output in 2 minutes. The two loading synchros areinterconnected, with the output of each being connected as a trackinginput signal to the other. The air supply to the respective loadingsynchros is controlled such that the selected synchro provides itsnormal output, while the other synchro tracks along, such that at anygiven time both synchros are at a position so that they provide the sameoutput. In this manner, selection can be switched from one to the otherat any time during loading or unloading. In this way a continuous loadsignal is maintained. Under normal operation, synchro 65L-2 (12 minute)is energized, 65L-1 being energized only when specifically selected orwhen a load hold or manual load point is desired.

In the discussion to follow, reference is also made to Table Dhereinbelow, which sets forth the operating conditions of a number ofthe subsystem components.

TABLE 1

196: pressure switch; contacts open when 65L output reaches 100%.

197: pressure switch; contacts open when 65L output reaches its minimumposition.

193: pressure switch; contacts close at 99% speed.

195: speed changer windback switch; contacts closed during windback, andopen at minimum output.

194: pressure switch; contacts open at full 65S output, to stop 65S.

201: pressure switch; starts speed changer at 50% speed.

RTLX: contacts close at ready to load.

52: switches at generator breaker closing.

37L: pressure switch; contacts open at MIN load.

As is seen in FIG. 22B, circuits S and T, this subsystem utilizes justone RAISE button and one LOWER button, each button being utilized forraising and lowering the speed control signal as well as the loadcontrol signal. Upon closing of the RAISE button 65RB, relay 65RX isenergized as long as the LOWER button 65LB is not closed. Conversely,when the LOWER 65LB button is pressed, relay 65LX is energized, on thecondition that the 65RX relay is not energized.

Operation of the overall speed and load control subsystem is derivedfrom the following operations:

1. When the MIN load button is pushed (see FIG. 13), normal start, thetwo 65L synchros stay at MIN position and the 65S synchro automaticallygoes to full position, 65SR being energized through circuit M untilcontacts 194 (6318S) are opened at the full speed synchro position. Thisautomatically allows 10% load. It is noted that in this operationneither 65RX nor 65LX is energized.

2. When the base load mode is selected (FIG. 13), normal start, 65L-2automatically goes to its full position, 65LR being energized throughcircuit C until contacts 196C open at full load signal (uponenergization of relay 196X). Synchro 65S goes to full output, 65SR beingenergized through circuit M until contacts 194 open at full output.(196X opens when contacts 196 open at full synchro speed output). Thispermits loading to the limit of the base temperature curve.

3. After the turbine is in the MIN load position, either the RAISE orLOWER button is pushed. This gives manual control of load synchro 65L-1,either through circuits B, C or B, E respectively. In either case, speedsynchro 65S goes to full position through circuit M.

4. All manual operation and selection of RAISE/LOWER automaticallyswitches to 65L-1.

5. After the system has been placed in the base load mode, pushingeither the RAISE or LOWER button causes grabbing manual control of 65Safter the load synchro reaches full output through circuit C. When itreaches this position, and the RAISE or LOWER button is pushed, relayTSLX is energized through circuit Q, and consequently either 65SL or65SR is energized through circuit I when the TSLX contacts there close.This permits manual raising or lowering of load on speed control. Whenthe turbine is at base, peak or system reserve load level, and the MINbutton is pushed, synchro 65L-1/65L-2 automatically goes to the MINlevel, due to energization of 65LL through circuit E.

6. At the same time, 65S stays up at its full level. This action permitsautomatic load reduction to the low limit. If manual control of65L-1/65L-2 has been previously obtained (by pushing MIN to get manualcontrol of 65L), and then MIN is pushed, no change in the position of65L takes place. If it is desired to return to MIN load, this must bedone manually. Once minimum load is reached, 65S goes to full output, ifnot already there.

7. If the turbine is on base, peak or system reserve control, and 65L isat full output, and then either the RAISE or LOWER button is pushed,manual control or 65S is obtained through circuit I, since contacts TSLXare then closed. 65L stays at full output, since 196X is open in circuitC.

8. When under normal manual control of 65S, and the MIN button ispushed, 65L automatically goes to the MIN position through circuit E,and is stopped when contacts 37LX open at MIN level (10%). Synchro 65Sstays where it was. This permits unit to be held at 10% load.

9. When under manual control of 65S, and MIN is momentarily pushed andthen base is re-pushed, 65L is already at full output (see 5 above), andstays there. 65S automatically goes to full where it is limited by theopening of contacts 194 though circuit M, thereby putting the turbine inbase temperature limit control.

10. When under manual control of 65L, and base is pushed, 65S is alreadyat full, and 65L automatically goes to full through circuit C, to get tobase temperature limit control.

11. When at base load, and either the RAISE or LOWER button is pushedafter also pushing MIN, (see 6 above), 65L starts to lower until either65LX or 65RX are closed in circuit P, thereby energizing MSLX andopening contacts MSLX in circuit E, thereby de-energizing 65L-1 to holdload at this level.

12. When in the base mode (65S and 65L are at full positions), and thenormal shutdown button (NSC) is pushed, 65L automatically returns to MINthrough circuits D, E to prepare for shutdown. 65S stays where it isuntil after shutdown.

13. When normal shutdown is pushed from any other position but base, 65Lautomatically goes back to the MIN position through circuits D, E, and65S stays where it was until after shutdown, or until it is manuallychanged through circuits J, L, or where the automatic synchronizer grabsit through circuit L.

14. If the shutdown cancel (NSC) is pushed at circuit Y, shutdown isinterrupted due to the opening of contacts 130 in circuit D.

15. If the generator circuit breaker opens on base, peak, system reserveor MIN mode, thus opening contacts 52, 65S returns to resync and reload,while 65L stays at full position.

The use of the speed-load control subsystem in operation can now bedescribed. The selectable options for load provision may be described asfollows:

A. Minimum--Initial 10% load step and manual load control from 0 to baseload. This position is used to hold load independent of system frequencychange.

B. Base Load--Initial 10% load step and ramp to preset base line as afunction of combustor pressure and turbine exhaust temperature. Partload operation can be had by reducing the speed reference andautomatically removing the machine from temperature control to speedcontrol by use of the speed/load lower button (after the unit hasreached temperature control as sensed by the loading synchro reachingfull position).

C. Peak Load--Initial 10% load step and ramp to preset peak line as afunction of combustor pressure and turbine exhaust temperature. Partload operation can be had by reducing the speed reference andautomatically removing the machine from temperature control to speedcontrol by use of the speed/load lower button (after the unit hasreached temperature control as sensed by the loading synchro reachingfull position).

D. System Reserve--Can only be selected after the generator breaker isclosed, and permits the unit to ramp to a pre-set system reserve line asa function of combustor pressure and exhaust temperature. Part loadoperation can be had by reducing the speed reference and automaticallyremoving the machine from temperature control to speed control by use ofthe speed/load lower button (after the unit as reached temperaturecontrol as sensed by loading synchro reaching full position).

In minimum control operation minimum is selected by the operator. The65S synchro motor is energized by the pressure switch at 50% speed, andproceeds until it is stopped at full output by a pressure switch 194.Operator control permits manual raise/lower control over synchro 65S topermit overspeed checkout of controls with the generator breaker open.At ready to load (98% speed) the synch circuit is armed. If the unitinterlocks are ready for synchronizing, the autosynch raise/lower pulsesbegin on 65S to match speeds. When synchronizing conditions are met, thegenerator breaker is automatically closed. Solenoid 187 (circuit W) isenergized to permit the 10% step to minimum power level, whatever hasbeen selected to accommodate a dead load pickup, within 25% of machinecapability. Synchro motor 65S drives to full position and de-energizes.The turbine is now under constant load control, with the power outputholding roughly constant with changing ambient temperature and linefrequency, even though speed varies to the low frequency or low speedlimit.

While under minimum control, if higher or lower load is required, thesubsystem provides for requesting a new setpoint by use of the commonraise/lower push buttons. Change in load is accomplished by energizing65L to a raised or lower output, the maximum output being limited bybase load temperature control and the minimum limited only by reversepower limitation.

If it is desired to establish the turbine on temperature control, theoperator, as in the earlier described embodiment, places the turbine ineither base, peak or system reserve mode of operation. On the commandfor one of the above load modes, 65L is driven automatically to its fullposition and de-energized. A temperature light corresponding to theselected control mode is illuminated. The selection of a temperaturecontrol mode nullifies load control and, after the load synchro reachesfull position, permits manual speed control reduction of the load.

When in base, peak or system reserve operation, it if is desirable toreduce load or to put the unit on speed control for load sharing fromthe temperature control mode, it can be accomplished by lowering modecontrol temperature via the common "LOWER" button until the controlsignal output is less than the temperature limit, thereby selectingspeed control as the controlling variable. The control acts to identifythis mode of operation by causing the speed control light to be lighted.

If it is desirable to return to the MIN position for maintenance of"Spinning Reserve", it is only necessary to reselect MIN position byselecting that button. At that time, the base, peak or system reservelight will be extinguished and the MIN position button lighted. Thecontrol system drives 65L to the MIN load position, where it isde-energized by 37LX. The 65S synchro remains at its pre-set conditionand can serve as a load limiter. If it is desired to go above it, theoperator may position to base and the 65S synchro will then autowind-out to full position.

Normal shutdown is achieved by selection of the normal shutdown button,which drives 65L to the minimum load. If the operator receives a chargefrom the dispatcher calling for load while programming back to MIN load,he may depress the "cancel" normal shutdown button. The control willthen re-ramp 65L it its full position, or can be stopped at thediscretion of the operator.

A unique feature built in to the control permits the operator by visualinspection to inhibit auto load decrease or increase from eithertemperature control (B, P, SR) to minimum (load control) or from MIN tobase (speed control), simply by depressing the raise or lower button tostop the auto movement of the required synchro (65L load control, 65Sspeed control).

The auto lock circuitry then anticipating manual control will permitmanual change in setpoint. Request for reautomation if in MIN ispermitted by pushing for Base, Peak or System Reserve.

If while operating at load the generator breaker trips, the machine isthen only sensitive to "SPEED CONTROL". At this point, the unitgenerator breaker will trip and the 65S synchro is returned by the autosynchronizer to the synchronous speed condition. Deactivation of theauto synchronizer will require that the operator return speed from 105%to the idle position for the next manual synchronizing.

As discussed above, there are two operator selectable automatic loadingand unloading rates, normal and fast. However, when the raise/lowerbuttons are pushed, the fast rate is automatically selected for manualload or speed control to give fast response from the push buttons. Theloading or unloading of the machine is at the operator's discretion.This ability to change at any time the loading rates (65L-1, 65L-2) isdue to the tracking feature described hereinabove.

If the unit is on speed control at part load (i.e., less than 100%)under manual control, the TSLX relay will be energized to inhibit theautomatic circuitry of 65S for manual over-riding. From this positionthe operator may return the unit to base, peak or system reserve limitby manually depressing the raise push button to cause 65S to drive toits full position. The travel of the 65S synchronous can be completed inas short as (20) seconds by the operator, but the load rate limiter willschedule load to the (2) minute loading rate.

The temp locking relay will remain energized and sealed until minimumload is selected or the breaker trips.

It if is desirable to release the lock relay and permit the unit toreload automatically to base, peak or system reserve, it is onlynecessary to momentarily push the MIN button and then the desiredloading button (B, P. SR). This action releases the TSLX lock andengages the auto circuit to drive the 65S synchro to its full position(as accomplished above on manual).

If the unit is on load control at part load under manual control, theMSLX relay will be energized to inhibit the automatic circuitry of 65Lfor manual over-riding. From this part load position, the operator mayraise the unit to base temperature limit manually by depressing theraise button to cause 65L to drive to its full position. If it isdesired to release the lock relay and permit the unit to loadautomatically to base, peak, or system reserve, it is only necessary tomomentarily push the desired selection button. This will cause releaseof the MSLX lock and engage the 65L synchro to its full position (asaccomplished above on manual).

Return to MIN load automatically from any partial load can beaccomplished by pushing base, peak, or system reserve momentarily, andthen re-pushing MIN position to cancel the TSLX lock and re-engage te65L synchro drive.

As discussed hereinabove, the load control path of the control system ofthis invention may be either open loop or closed loop. FIG. 23Aillustrates the essential components of the load and speed controlpaths, for the closed loop system. Pressure switches 196 and 194 limitthe outputs of load synchro 65L and speed synchro 65S respectively. FIG.23B shows a modification of the apparatus for providing the reset signalto load controller 265, where the closed loop load control is used withthe speed/load hold the lock system. In this case, the load synchro 65Lis replaced with two load synchros, 65L-1 and 65L-2, each adapted totrack the selected one, and providing 2 minute and 12 minute rampsrespectively. Air is supplied to the selected load synchro throughsolenoid valve FL-S, and the tracking synchro input is shunted from theair supply by valve FL-A, which vents the input of the tracking synchroto atmosphere. Thus, when 65L-1 is chosen, both FL-S and FL-A arede-energized, such that air is supplied to 65L-1 and the input to 65L-2is vented to atmospheric pressure. When 65L-2 is chosen, both FL-S andFL-A are energized. However, the tracking inputs T-1, T-2 enable thenon-selected synchro to track the chosen synchro, such that switchoverfrom one to the other can be effected immediately.

Operation of the closed loop load and speed control, combined with thespeed/load hold and lock system described hereinabove, providessubstantially infinite adjustability of load on either side or loadcontrol. When minimum load is called for, manual control of 65L-1 iseither ascending or descending direction is obtainable. Correspondingly,when base load is called for by pushing the base switch, manual control65S is obtainable. The maximum points of 65S and 65L-1, 65L-2 areinterlocked by contacts 194 and 196 respectively.

H. MONITORING SYSTEM

The turbine power plant of this invention has, as a necessary adjunct tothe control system, a monitoring system which provides display, alarmand shutdown functions. Portions of such monitoring system have beendescribed hereinbefore. In particular, with regard to the two shotfeature described hereinabove, reference was made to monitoring bearingtemperature and exhaust temperature. A disclosure has also been made ofthe means provided for displaying which control path is generating thelow select signal. Table 2 below presents a partial list of alarm andshutdown functions carried out by the turbine monitoring system of thisinvention.

                                      TABLE 2                                     __________________________________________________________________________    ALARM AND SHUTDOWN FUNCTIONS                                                           LOCAL    REMOTE   2   1                                              NAME     START                                                                              RUN START                                                                              RUN SHOT                                                                              SHOT                                                                              ALARM SETTING                              __________________________________________________________________________    BP START                                                                      OT#1*    SD   --  SD   --      X                                                                                 X   1300° F.                        BP START                                                                      OT#2*    SD   --  SD   --      X                                              BP RUN*  SD   SD  SD   SD  X                                                                                     X   1080° F.                        BP RUN*  SD   SD  SD   SD  X                                                  BP DIFF                            X   100° F.                         TURB EXH.*                                                                             SD   SD  SD   SD  X                                                                                     X   1050° F.                        TURB EXH.*                                                                             SD   SD  SD   SD  X                                                  TURB EXH.                                                                     DIFF     A    A   A    A               100° F.                         DISC CAVITY                                                                            A    A   A    A           X                                          LOW LUBE SD   SD  SD   SD  X       X                                          HI GAS                                                                        PRESS             Permissive                                                                                     X                                           LOW GAS                                                                      PRESS    SD   SD  SD   SD  X                                                  TURB                                                                          OVERSPD  SD   SD  SD   SD  X       X                                          110 VDC  SD   SD  SD   SD  X       X                                          VB1-S VI-                                                                     BRATION                                                                       (5M)     A    --  SD   --  X       X                                          VB1-R ABOVE                                                                   95% N (3M)                                                                             --   A   --   SD  X       X                                          VB1-0 OPEN                                                                    P.V.     A    A   A    A           X                                          (for each                                                                     monitored                                                                     position)                                                                     BEARING  SD   SD  SD   SD      X   X   200° F.                         BEARING  SD   SD  SD   SD      X   X   230° F.                         BEARING  SD   SD  SD   SD      X   X   230° F.                         BEARING  SD   SD  SD   SD      X   X   230° F.                         BEARING  SD   SD  SD   SD      X   X   170° F.                         BEARING  SD   SD  SD   SD      X   X   170° F.                         LUBE LEVEL                                                                             A    A   SD   SD  X       X   --                                     BRG. OIL                                                                      TEMP     A    A   SD   SD  X       X   140° F.                         SPD SYST                                                                      FAILURE  A    A   A    A           X   5% Diff.                               7A OUTFIRE*                                                                            SD   SD  SD   SD  X                                                                                     X   (option 1,                             8A OUTFIRE*                                                                            SD   SD  SD   SD  X           2, 3 tries)                            7B OUTFIRE*                                                                            SD   SD  SD   SD  X                                                                                     X                                          8B OUTFIRE*                                                                            SD   SD  SD   SD  X                                                  __________________________________________________________________________     *Takes one to alarm, two to shut down.                                   

From inspection of Table 2, it is seen that control can be maintained bythe operator at either a local or remote station. Depending upon thepoint of control, alarm and/or shutdown functions may be scheduleddifferently. In addition, any given function may be subject to one-shot,two-shot, or n-shot control, where n is any number of shots that theuser may want to have available. The system provides completeflexibility in providing which functions are to be subject to 2-shot orn-shot control. Further, the alarm and shutdown functions may be madedependent upon predetermined ranges of operation. As shown in the Table,the alarm and shutdown functions may be varied depending upon whetherthe turbine is in the start mode of operation or run mode. This may beaccomplished either by plural sensing circuits, or sensing circuitswhich are switchable upon passage of the turbine from one operatingpoint to a next, such that the alarm or shutdown loop is switched fromthe single shot to two shot form of operation, or vice versa.

The design philosophy of the control system and the monitoring system ofthis invention is that of providing "load availability", i.e., to makeevery effort to continue supplying power. To meet this need it isimperative that turbine shutdown occur only in response to actualshutdown conditions, and be prevented unless damage is probable. It isalso necessary that the control scheme alert the operator, withoutcausing shutdown, when it is the monitoring system or control systemitself which is malfunctioning, i.e., when sensor or component failurescause the alarm. In such cases, it is highly desirable to provide amaximum amount of information to the operator without interrupting loadavailability.

Two basic approaches to obtaining reliability in a monitoring circuitare seen in examples set forth in this disclosure. The designillustrated in the exhaust and blade path circuits, FIG. 6A, involvesplural hardware paths with auctioneering selection of designateddirection of failure for the final output signal. This approach is basedupon the premise that, when the hardware fails, it fails in a designateddirection. Specifically, the high pressure select element effectivelyeliminates the path containing a failure, and selects the high signalpath which presumably does not contain a failure. It is understood thatthis approach, by its nature, is not a "fail safe" approach, since bothpaths may be producing erroneously low signals. In the "fail safe" typeof design, the monitored condition must be properly sensed by aplurality of sensors, and if any one of the sensor paths fails, failureis indicated. Reliability of this approach can be improved by completeredundancy of each given sensor function. Thus, in the disc cavityprotection circuit of this turbine control system thermocouple pairs areutilized with paralleling of the final output contacts. The parallelcontact pairs are in turn connected in series so that, if any one of thethermocouple pairs fails open, shutdown is caused. However, thereremains a great requirement for a compromise design between the non-failsafe drive direction arrangement which negates any possible shutdown,and the fail safe arrangement which causes shutdown, and thereforenon-availability.

Referring now to FIGS. 26A and 26B, there is illustrated a uniqueapparatus and method which achieves the desired compromise, and whichclearly distinguishes the existence of an alarm condition from acondition of component or thermocouple failure, without causingshutdown. In the embodiment shown, there is provided an operationalamplifier 404 having inputs connected to a thermocouple (designatedT/C). The input to the operational amplifier is adjusted by positioningvariable resistor 401, and the downdrive (thermocouple open) input isconnected at terminal 403. The output of the operational amplifier isconnected to a pair of comparators 409 and 410 having setpointadjustment resistors 406 and 407 respectively connected between theirinputs and ground. The output of the comparators are connected to relays411 and 412 respectively. In addition, the output of comparator 409 isconnected through normally closed contacts 411-1 to an indicator 414,and the output of comparator 410 is connected through normally closedcontacts 412-1 to indicator 415. Normally open output contacts 411-2 and412-2, operated by relays 411 and 412 respectively, provide the alarm(or shutdown) outputs.

The operation of the arrangement of 26B is understood in conjunctionwith FIG. 26A, showing a typical characteristic of a thermocouple. Whenan actual alarm condition is reached, e.g., over temperature in abearing protection circuit, the high alarm setpoint is reached, causingan output at comparator 409. This energizes relay 411, thus openingcontacts 411-1 and turning off light 414, and closing contacts 411-2 toprovide the alarm signal. This alarm signal is unequivocal, andrepresents a high alarm condition.

In the event of thermocouple open, or failure elsewhere in theelectronic circuitry, the operational amplifier is driven to negativesaturation. The setpoint adjustment resistor 407 is set to a temperatureequivalent of -50° F., to establish a "non-reasonable" condition that isdistinct from the high setpoint alarm condition, and which would notreasonably be reached under operating conditions since -50° F. is out ofthe normal range of expected temperature. Consequently, utilization ofthis setpoint does not subject the control arrangement to nuisancealarming which would be the expected response from any typicaltemperature control having a setpoint in the operating range. Uponthermocouple or component failure, the output of operational amplifier404 drops below the -50° F. setpoint, causing an output from comparator410. This in turn energizes relay 412 and opens contacts 412-1, thusturning off the indicator light 415. In addition, contacts 412-2 areclosed, providing the alarm failure. When this alarm failure occurs, theoperator can see that light 414 remains on, and that consequently thehigh condition has not been reached but that there is thermocouple orother component failure. The circuit thus provides an unambiguousrepresentation of the type of failure which has been sensed, andprovides the desired compromise between the fail safe and non-fail safetype of monitoring arrangements.

From the above, it is seen that there is disclosed a gas turbineelectric power plant having a control system which possesses a logiccapability comparable to digital computer-controlled systems, but havingreliability and adaptability features which are an improvement overpresent digital control systems. In the turbine control system of thisinvention, each of the separate control paths has a continuouslyoperating and independent turbine-control system interface. The controlsystem is structured with a modularity that permits great flexibility indesign and provides for an enhanced visual output, or indication to theoperator of system conditions. Thus, while the preferred embodiment ofthe control system as illustrated is pneumatic, the entire system, ordiscrete portions thereof, may be constructed in alternate forms, e.g.,solid state electronic hardware. Each of the illustrated control loops,as well as the temperature reset starting control subsystem, whereinfunction generators are utilized, can be adapted to use solid statecomponents, if desired. As used herein to describe portions of thecontrol system, the term modular means that the portion as a unit (ormodule) can be replaced with a unit which is different structurally, butwhich performs the same function, and without impairment of the controlsystem display.

It is also to be noted that many of the unique features of the controlsystem of this invention may be incorporated in digital, or softwareform. Thus, the logic and scheduling steps of the illustrated bearingprotective subsystem may be carried out by a programmed digitalcomputer, with suitable conventional interface between the turbine andthe subsystem. In a similar manner, the "pop and glide" sequence controland the "two shot" method of automatic restart after shutdown can becarried out with equivalent software means. The speed-load hold and locksystem has likewise been described in an electronic-pneumatic form, butmay be embodied in software form.

What is claimed is:
 1. A gas turbine electric power plant including agas turbine having compressor, combustion and turbine elements, agenerator coupled to the gas turbine for drive power, a generatorbreaker for coupling said generator to a power system so as to deliverpower to the power system, a fuel system for supplying fuel to said gasturbine combustion element, and a turbine load control system forcontrolling the load accepted by said turbine, said turbine load controlsystem comprising:a. a first control path for generating a first controlsignal adaptable to control the acceptance of turbine load according toa first predetermined schedule; b. a second control path for generatinga second control signal adaptable to control the acceptance of turbineload according to a second schedule, and having means for selectivelyinitiating generation of said second control signal in accordance withoperator choice; c. said second control path including means forselecting the rate of change of said generated second control signalfrom a plurality of rates; d. means for comparing said control signalsin accordance with a predetermined arrangement, and for providing aturbine load acceptance control signal derived from said comparison; ande. means for operating said fuel system with said derived turbine loadacceptance control signal to schedule the acceptance of turbine loadafter generator breaker closing.
 2. The turbine load acceptance controlsystem as set forth in claim 1 additionally comprising means forautomatically limiting turbine load at a given level.
 3. The turbineload acceptance control system as set forth in claim 2 wherein saidmeans for limiting turbine load includes means for generating at leastone signal which is a function of the temperature at a predeterminedportion of said turbine, and wherein said comparing means also comparessaid temperature signal with said first and second control signals, andderives said turbine load acceptance control signal as a function ofsaid comparison.
 4. The turbine load acceptance control system as setforth in claim 3 wherein said load limiting means limits acceptedturbine load to a level which is commensurate with said temperaturesignal if said temperature signal is derived as said turbine loadacceptance control signal.
 5. The turbine load acceptance control systemas set forth in claim 4 wherein said means for generating at least onesignal includes means for adapting said temperature signal to correspondto one of a plurality of acceptable load levels.
 6. The turbine loadacceptance control system as set forth in claim 5 further comprisingmeans for manually controlling generation of one of said controlsignals, thereby manually controlling load change.
 7. The turbine loadacceptance control system as set forth in claim 6 further comprisingmeans for initiation of generation of said first control signal prior togenerator breaker closing, and wherein said operating means operatessaid fuel supply system with said first control signal to scheduleturbine speed prior to generator breaker closing.
 8. The turbine loadacceptance control system as set forth in claim 7 comprising means forchanging said first control signal at generator breaker closing, so asto enable said turbine to accept load at generator breaker closing. 9.The turbine load acceptance control system as set forth in claim 1wherein said initiation means is adapted to initiate generation of saidsecond signal at generator breaker closing.
 10. The turbine loadacceptance control system as set forth in claim 9 wherein said first andsecond control signals are substantially the same just after breakerclosing and said second control signal is changed at a rate relative tosaid first control signal so that it controls the turbine loading aftergenerator breaker closing.
 11. A gas turbine electric power plantincluding a gas turbine having compressor, combustion and turbineelements, a generator coupled to the gas turbine for drive power, agenerator breaker for coupling said generator to a power system so as todeliver power to the power system, a fuel system for supplying fuel tosaid gas turbine combustion element, and a turbine load control systemfor controlling the load accepted by said turbine, said turbine loadcontrol system comprising:a. a first closed loop control path forgenerating a first control signal adaptable to control the acceptance ofturbine load according to a first predetermined schedule; b. a secondclosed loop control path for generating a second control signaladaptable to control the acceptance of turbine load according to asecond schedule, and having means for selectively initiating generationof said second control signal in accordance with operator choice; c.said second closed loop control path including means for selecting therate of change of said generated second control signal from a pluralityof rates; d. means for comparing said control signals in accordance witha predetermined arrangement, and for providing a turbine load acceptancecontrol signal derived from said comparison; and e. means for operatingsaid fuel system with said derived turbine load acceptance controlsignal to schedule the acceptance of turbine load after generatorbreaker closing.
 12. The turbine load acceptance control system as setforth in claim 11 additionally comprising means for automaticallylimiting turbine load at a given level.
 13. The turbine load acceptancecontrol system as set forth in claim 12 wherein said means for limitingturbine load includes means for generating at least one signal which isa function of the temperature at a predetermined portion of saidturbine, and wherein said comparing means also compares said temperaturesignal with said first and second control signals, and derives saidturbine load acceptance control signal as a function of said comparison.14. The turbine load acceptance control system as set forth in claim 13wherein said load limiting means limits accepted turbine load to a levelwhich is commensurate with said temperature signal if said temperaturesignal is derived as said turbine load acceptance control signal. 15.The turbine load acceptance control system as set forth in claim 14wherein said means for generating at least one signal includes means foradapting said temperature signal to correspond to one of a plurality ofacceptable load levels.
 16. The turbine load acceptance control systemas set forth in claim 15 further comprising means for manuallycontrolling generation of one of said control signals, thereby manuallycontrolling load change.
 17. The turbine load acceptance control systemas set forth in claim 16 further comprising means for initiation ofgeneration of said first control signal prior to generator breakerclosing, and wherein said operating means operates said fuel supplysystem with said first control signal to schedule turbine speed prior togenerator breaker closing.
 18. The turbine load acceptance controlsystem as set forth in claim 17 comprising means for changing said firstcontrol signal at generator breaker closing, so as to enable saidturbine to accept load at generator breaker closing.
 19. The turbineload acceptance control system as set forth in claim 11 wherein saidinitiation means is adapted to initiate generation of said second signalat generator breaker closing.
 20. The turbine load acceptance controlsystem as set forth in claim 19 wherein said first and second controlsignals are substantially the same just after breaker closing and saidsecond control signal is changed at a rate relative to said firstcontrol signal so that it controls the turbine loading after generatorbreaker closing.